1 ========================
2 Building LLVM with CMake
3 ========================
11 `CMake <http://www.cmake.org/>`_ is a cross-platform build-generator tool. CMake
12 does not build the project, it generates the files needed by your build tool
13 (GNU make, Visual Studio, etc.) for building LLVM.
15 If you are really anxious about getting a functional LLVM build, go to the
16 `Quick start`_ section. If you are a CMake novice, start with `Basic CMake usage`_
17 and then go back to the `Quick start`_ section once you know what you are doing. The
18 `Options and variables`_ section is a reference for customizing your build. If
19 you already have experience with CMake, this is the recommended starting point.
26 We use here the command-line, non-interactive CMake interface.
28 #. `Download <http://www.cmake.org/cmake/resources/software.html>`_ and install
29 CMake. Version 2.8.8 is the minimum required.
31 #. Open a shell. Your development tools must be reachable from this shell
32 through the PATH environment variable.
34 #. Create a build directory. Building LLVM in the source
35 directory is not supported. cd to this directory:
37 .. code-block:: console
42 #. Execute this command in the shell replacing `path/to/llvm/source/root` with
43 the path to the root of your LLVM source tree:
45 .. code-block:: console
47 $ cmake path/to/llvm/source/root
49 CMake will detect your development environment, perform a series of tests, and
50 generate the files required for building LLVM. CMake will use default values
51 for all build parameters. See the `Options and variables`_ section for
52 a list of build parameters that you can modify.
54 This can fail if CMake can't detect your toolset, or if it thinks that the
55 environment is not sane enough. In this case, make sure that the toolset that
56 you intend to use is the only one reachable from the shell, and that the shell
57 itself is the correct one for your development environment. CMake will refuse
58 to build MinGW makefiles if you have a POSIX shell reachable through the PATH
59 environment variable, for instance. You can force CMake to use a given build
60 tool; for instructions, see the `Usage`_ section, below.
62 #. After CMake has finished running, proceed to use IDE project files, or start
63 the build from the build directory:
65 .. code-block:: console
69 The ``--build`` option tells ``cmake`` to invoke the underlying build
70 tool (``make``, ``ninja``, ``xcodebuild``, ``msbuild``, etc.)
72 The underlying build tool can be invoked directly, of course, but
73 the ``--build`` option is portable.
75 #. After LLVM has finished building, install it from the build directory:
77 .. code-block:: console
79 $ cmake --build . --target install
81 The ``--target`` option with ``install`` parameter in addition to
82 the ``--build`` option tells ``cmake`` to build the ``install`` target.
84 It is possible to set a different install prefix at installation time
85 by invoking the ``cmake_install.cmake`` script generated in the
88 .. code-block:: console
90 $ cmake -DCMAKE_INSTALL_PREFIX=/tmp/llvm -P cmake_install.cmake
92 .. _Basic CMake usage:
98 This section explains basic aspects of CMake
99 which you may need in your day-to-day usage.
101 CMake comes with extensive documentation, in the form of html files, and as
102 online help accessible via the ``cmake`` executable itself. Execute ``cmake
103 --help`` for further help options.
105 CMake allows you to specify a build tool (e.g., GNU make, Visual Studio,
106 or Xcode). If not specified on the command line, CMake tries to guess which
107 build tool to use, based on your environment. Once it has identified your
108 build tool, CMake uses the corresponding *Generator* to create files for your
109 build tool (e.g., Makefiles or Visual Studio or Xcode project files). You can
110 explicitly specify the generator with the command line option ``-G "Name of the
111 generator"``. To see a list of the available generators on your system, execute
113 .. code-block:: console
117 This will list the generator names at the end of the help text.
119 Generators' names are case-sensitive, and may contain spaces. For this reason,
120 you should enter them exactly as they are listed in the ``cmake --help``
121 output, in quotes. For example, to generate project files specifically for
122 Visual Studio 12, you can execute:
124 .. code-block:: console
126 $ cmake -G "Visual Studio 12" path/to/llvm/source/root
128 For a given development platform there can be more than one adequate
129 generator. If you use Visual Studio, "NMake Makefiles" is a generator you can use
130 for building with NMake. By default, CMake chooses the most specific generator
131 supported by your development environment. If you want an alternative generator,
132 you must tell this to CMake with the ``-G`` option.
136 Explain variables and cache. Move explanation here from #options section.
138 .. _Options and variables:
140 Options and variables
141 =====================
143 Variables customize how the build will be generated. Options are boolean
144 variables, with possible values ON/OFF. Options and variables are defined on the
145 CMake command line like this:
147 .. code-block:: console
149 $ cmake -DVARIABLE=value path/to/llvm/source
151 You can set a variable after the initial CMake invocation to change its
152 value. You can also undefine a variable:
154 .. code-block:: console
156 $ cmake -UVARIABLE path/to/llvm/source
158 Variables are stored in the CMake cache. This is a file named ``CMakeCache.txt``
159 stored at the root of your build directory that is generated by ``cmake``.
160 Editing it yourself is not recommended.
162 Variables are listed in the CMake cache and later in this document with
163 the variable name and type separated by a colon. You can also specify the
164 variable and type on the CMake command line:
166 .. code-block:: console
168 $ cmake -DVARIABLE:TYPE=value path/to/llvm/source
170 Frequently-used CMake variables
171 -------------------------------
173 Here are some of the CMake variables that are used often, along with a
174 brief explanation and LLVM-specific notes. For full documentation, consult the
175 CMake manual, or execute ``cmake --help-variable VARIABLE_NAME``.
177 **CMAKE_BUILD_TYPE**:STRING
178 Sets the build type for ``make``-based generators. Possible values are
179 Release, Debug, RelWithDebInfo and MinSizeRel. If you are using an IDE such as
180 Visual Studio, you should use the IDE settings to set the build type.
182 **CMAKE_INSTALL_PREFIX**:PATH
183 Path where LLVM will be installed if "make install" is invoked or the
184 "install" target is built.
186 **LLVM_LIBDIR_SUFFIX**:STRING
187 Extra suffix to append to the directory where libraries are to be
188 installed. On a 64-bit architecture, one could use ``-DLLVM_LIBDIR_SUFFIX=64``
189 to install libraries to ``/usr/lib64``.
191 **CMAKE_C_FLAGS**:STRING
192 Extra flags to use when compiling C source files.
194 **CMAKE_CXX_FLAGS**:STRING
195 Extra flags to use when compiling C++ source files.
197 **BUILD_SHARED_LIBS**:BOOL
198 Flag indicating if shared libraries will be built. Its default value is
199 OFF. This option is only recommended for use by LLVM developers.
200 On Windows, shared libraries may be used when building with MinGW, including
201 mingw-w64, but not when building with the Microsoft toolchain.
203 .. _LLVM-specific variables:
205 LLVM-specific variables
206 -----------------------
208 **LLVM_TARGETS_TO_BUILD**:STRING
209 Semicolon-separated list of targets to build, or *all* for building all
210 targets. Case-sensitive. Defaults to *all*. Example:
211 ``-DLLVM_TARGETS_TO_BUILD="X86;PowerPC"``.
213 **LLVM_BUILD_TOOLS**:BOOL
214 Build LLVM tools. Defaults to ON. Targets for building each tool are generated
215 in any case. You can build a tool separately by invoking its target. For
216 example, you can build *llvm-as* with a Makefile-based system by executing *make
217 llvm-as* at the root of your build directory.
219 **LLVM_INCLUDE_TOOLS**:BOOL
220 Generate build targets for the LLVM tools. Defaults to ON. You can use this
221 option to disable the generation of build targets for the LLVM tools.
223 **LLVM_BUILD_EXAMPLES**:BOOL
224 Build LLVM examples. Defaults to OFF. Targets for building each example are
225 generated in any case. See documentation for *LLVM_BUILD_TOOLS* above for more
228 **LLVM_INCLUDE_EXAMPLES**:BOOL
229 Generate build targets for the LLVM examples. Defaults to ON. You can use this
230 option to disable the generation of build targets for the LLVM examples.
232 **LLVM_BUILD_TESTS**:BOOL
233 Build LLVM unit tests. Defaults to OFF. Targets for building each unit test
234 are generated in any case. You can build a specific unit test using the
235 targets defined under *unittests*, such as ADTTests, IRTests, SupportTests,
236 etc. (Search for ``add_llvm_unittest`` in the subdirectories of *unittests*
237 for a complete list of unit tests.) It is possible to build all unit tests
238 with the target *UnitTests*.
240 **LLVM_INCLUDE_TESTS**:BOOL
241 Generate build targets for the LLVM unit tests. Defaults to ON. You can use
242 this option to disable the generation of build targets for the LLVM unit
245 **LLVM_APPEND_VC_REV**:BOOL
246 Append version control revision info (svn revision number or Git revision id)
247 to LLVM version string (stored in the PACKAGE_VERSION macro). For this to work
248 cmake must be invoked before the build. Defaults to OFF.
250 **LLVM_ENABLE_THREADS**:BOOL
251 Build with threads support, if available. Defaults to ON.
253 **LLVM_ENABLE_CXX1Y**:BOOL
254 Build in C++1y mode, if available. Defaults to OFF.
256 **LLVM_ENABLE_ASSERTIONS**:BOOL
257 Enables code assertions. Defaults to ON if and only if ``CMAKE_BUILD_TYPE``
260 **LLVM_ENABLE_EH**:BOOL
261 Build LLVM with exception-handling support. This is necessary if you wish to
262 link against LLVM libraries and make use of C++ exceptions in your own code
263 that need to propagate through LLVM code. Defaults to OFF.
265 **LLVM_ENABLE_PIC**:BOOL
266 Add the ``-fPIC`` flag to the compiler command-line, if the compiler supports
267 this flag. Some systems, like Windows, do not need this flag. Defaults to ON.
269 **LLVM_ENABLE_RTTI**:BOOL
270 Build LLVM with run-time type information. Defaults to OFF.
272 **LLVM_ENABLE_WARNINGS**:BOOL
273 Enable all compiler warnings. Defaults to ON.
275 **LLVM_ENABLE_PEDANTIC**:BOOL
276 Enable pedantic mode. This disables compiler-specific extensions, if
277 possible. Defaults to ON.
279 **LLVM_ENABLE_WERROR**:BOOL
280 Stop and fail the build, if a compiler warning is triggered. Defaults to OFF.
282 **LLVM_ABI_BREAKING_CHECKS**:STRING
283 Used to decide if LLVM should be built with ABI breaking checks or
284 not. Allowed values are `WITH_ASSERTS` (default), `FORCE_ON` and
285 `FORCE_OFF`. `WITH_ASSERTS` turns on ABI breaking checks in an
286 assertion enabled build. `FORCE_ON` (`FORCE_OFF`) turns them on
287 (off) irrespective of whether normal (`NDEBUG`-based) assertions are
288 enabled or not. A version of LLVM built with ABI breaking checks
289 is not ABI compatible with a version built without it.
291 **LLVM_BUILD_32_BITS**:BOOL
292 Build 32-bit executables and libraries on 64-bit systems. This option is
293 available only on some 64-bit Unix systems. Defaults to OFF.
295 **LLVM_TARGET_ARCH**:STRING
296 LLVM target to use for native code generation. This is required for JIT
297 generation. It defaults to "host", meaning that it shall pick the architecture
298 of the machine where LLVM is being built. If you are cross-compiling, set it
299 to the target architecture name.
301 **LLVM_TABLEGEN**:STRING
302 Full path to a native TableGen executable (usually named ``llvm-tblgen``). This is
303 intended for cross-compiling: if the user sets this variable, no native
304 TableGen will be created.
306 **LLVM_LIT_ARGS**:STRING
307 Arguments given to lit. ``make check`` and ``make clang-test`` are affected.
308 By default, ``'-sv --no-progress-bar'`` on Visual C++ and Xcode, ``'-sv'`` on
311 **LLVM_LIT_TOOLS_DIR**:PATH
312 The path to GnuWin32 tools for tests. Valid on Windows host. Defaults to
313 the empty string, in which case lit will look for tools needed for tests
314 (e.g. ``grep``, ``sort``, etc.) in your %PATH%. If GnuWin32 is not in your
315 %PATH%, then you can set this variable to the GnuWin32 directory so that
316 lit can find tools needed for tests in that directory.
318 **LLVM_ENABLE_FFI**:BOOL
319 Indicates whether the LLVM Interpreter will be linked with the Foreign Function
320 Interface library (libffi) in order to enable calling external functions.
321 If the library or its headers are installed in a custom
322 location, you can also set the variables FFI_INCLUDE_DIR and
323 FFI_LIBRARY_DIR to the directories where ffi.h and libffi.so can be found,
324 respectively. Defaults to OFF.
326 **LLVM_EXTERNAL_{CLANG,LLD,POLLY}_SOURCE_DIR**:PATH
327 These variables specify the path to the source directory for the external
328 LLVM projects Clang, lld, and Polly, respectively, relative to the top-level
329 source directory. If the in-tree subdirectory for an external project
330 exists (e.g., llvm/tools/clang for Clang), then the corresponding variable
331 will not be used. If the variable for an external project does not point
332 to a valid path, then that project will not be built.
334 **LLVM_USE_OPROFILE**:BOOL
335 Enable building OProfile JIT support. Defaults to OFF.
337 **LLVM_USE_INTEL_JITEVENTS**:BOOL
338 Enable building support for Intel JIT Events API. Defaults to OFF.
340 **LLVM_ENABLE_ZLIB**:BOOL
341 Enable building with zlib to support compression/uncompression in LLVM tools.
344 **LLVM_USE_SANITIZER**:STRING
345 Define the sanitizer used to build LLVM binaries and tests. Possible values
346 are ``Address``, ``Memory``, ``MemoryWithOrigins``, ``Undefined``, ``Thread``,
347 and ``Address;Undefined``. Defaults to empty string.
349 **LLVM_PARALLEL_COMPILE_JOBS**:STRING
350 Define the maximum number of concurrent compilation jobs.
352 **LLVM_PARALLEL_LINK_JOBS**:STRING
353 Define the maximum number of concurrent link jobs.
355 **LLVM_BUILD_DOCS**:BOOL
356 Enables all enabled documentation targets (i.e. Doxgyen and Sphinx targets) to
357 be built as part of the normal build. If the ``install`` target is run then
358 this also enables all built documentation targets to be installed. Defaults to
361 **LLVM_ENABLE_DOXYGEN**:BOOL
362 Enables the generation of browsable HTML documentation using doxygen.
365 **LLVM_ENABLE_DOXYGEN_QT_HELP**:BOOL
366 Enables the generation of a Qt Compressed Help file. Defaults to OFF.
367 This affects the make target ``doxygen-llvm``. When enabled, apart from
368 the normal HTML output generated by doxygen, this will produce a QCH file
369 named ``org.llvm.qch``. You can then load this file into Qt Creator.
370 This option is only useful in combination with ``-DLLVM_ENABLE_DOXYGEN=ON``;
371 otherwise this has no effect.
373 **LLVM_DOXYGEN_QCH_FILENAME**:STRING
374 The filename of the Qt Compressed Help file that will be generated when
375 ``-DLLVM_ENABLE_DOXYGEN=ON`` and
376 ``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON`` are given. Defaults to
378 This option is only useful in combination with
379 ``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON``;
380 otherwise it has no effect.
382 **LLVM_DOXYGEN_QHP_NAMESPACE**:STRING
383 Namespace under which the intermediate Qt Help Project file lives. See `Qt
385 for more information. Defaults to "org.llvm". This option is only useful in
386 combination with ``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON``; otherwise
389 **LLVM_DOXYGEN_QHP_CUST_FILTER_NAME**:STRING
390 See `Qt Help Project`_ for
391 more information. Defaults to the CMake variable ``${PACKAGE_STRING}`` which
392 is a combination of the package name and version string. This filter can then
393 be used in Qt Creator to select only documentation from LLVM when browsing
394 through all the help files that you might have loaded. This option is only
395 useful in combination with ``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON``;
396 otherwise it has no effect.
398 .. _Qt Help Project: http://qt-project.org/doc/qt-4.8/qthelpproject.html#custom-filters
400 **LLVM_DOXYGEN_QHELPGENERATOR_PATH**:STRING
401 The path to the ``qhelpgenerator`` executable. Defaults to whatever CMake's
402 ``find_program()`` can find. This option is only useful in combination with
403 ``-DLLVM_ENABLE_DOXYGEN_QT_HELP=ON``; otherwise it has no
406 **LLVM_DOXYGEN_SVG**:BOOL
407 Uses .svg files instead of .png files for graphs in the Doxygen output.
410 **LLVM_ENABLE_SPHINX**:BOOL
411 If enabled CMake will search for the ``sphinx-build`` executable and will make
412 the ``SPHINX_OUTPUT_HTML`` and ``SPHINX_OUTPUT_MAN`` CMake options available.
415 **SPHINX_EXECUTABLE**:STRING
416 The path to the ``sphinx-build`` executable detected by CMake.
418 **SPHINX_OUTPUT_HTML**:BOOL
419 If enabled (and ``LLVM_ENABLE_SPHINX`` is enabled) then the targets for
420 building the documentation as html are added (but not built by default unless
421 ``LLVM_BUILD_DOCS`` is enabled). There is a target for each project in the
422 source tree that uses sphinx (e.g. ``docs-llvm-html``, ``docs-clang-html``
423 and ``docs-lld-html``). Defaults to ON.
425 **SPHINX_OUTPUT_MAN**:BOOL
426 If enabled (and ``LLVM_ENABLE_SPHINX`` is enabled) the targets for building
427 the man pages are added (but not built by default unless ``LLVM_BUILD_DOCS``
428 is enabled). Currently the only target added is ``docs-llvm-man``. Defaults
431 **SPHINX_WARNINGS_AS_ERRORS**:BOOL
432 If enabled then sphinx documentation warnings will be treated as
433 errors. Defaults to ON.
435 Executing the test suite
436 ========================
438 Testing is performed when the *check-all* target is built. For instance, if you are
439 using Makefiles, execute this command in the root of your build directory:
441 .. code-block:: console
445 On Visual Studio, you may run tests by building the project "check-all".
446 For more information about testing, see the :doc:`TestingGuide`.
451 See `this wiki page <http://www.vtk.org/Wiki/CMake_Cross_Compiling>`_ for
452 generic instructions on how to cross-compile with CMake. It goes into detailed
453 explanations and may seem daunting, but it is not. On the wiki page there are
454 several examples including toolchain files. Go directly to `this section
455 <http://www.vtk.org/Wiki/CMake_Cross_Compiling#Information_how_to_set_up_various_cross_compiling_toolchains>`_
456 for a quick solution.
458 Also see the `LLVM-specific variables`_ section for variables used when
461 Embedding LLVM in your project
462 ==============================
464 From LLVM 3.5 onwards both the CMake and autoconf/Makefile build systems export
465 LLVM libraries as importable CMake targets. This means that clients of LLVM can
466 now reliably use CMake to develop their own LLVM-based projects against an
467 installed version of LLVM regardless of how it was built.
469 Here is a simple example of a CMakeLists.txt file that imports the LLVM libraries
470 and uses them to build a simple application ``simple-tool``.
472 .. code-block:: cmake
474 cmake_minimum_required(VERSION 2.8.8)
475 project(SimpleProject)
477 find_package(LLVM REQUIRED CONFIG)
479 message(STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
480 message(STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
482 # Set your project compile flags.
483 # E.g. if using the C++ header files
484 # you will need to enable C++11 support
487 include_directories(${LLVM_INCLUDE_DIRS})
488 add_definitions(${LLVM_DEFINITIONS})
490 # Now build our tools
491 add_executable(simple-tool tool.cpp)
493 # Find the libraries that correspond to the LLVM components
494 # that we wish to use
495 llvm_map_components_to_libnames(llvm_libs support core irreader)
497 # Link against LLVM libraries
498 target_link_libraries(simple-tool ${llvm_libs})
500 The ``find_package(...)`` directive when used in CONFIG mode (as in the above
501 example) will look for the ``LLVMConfig.cmake`` file in various locations (see
502 cmake manual for details). It creates a ``LLVM_DIR`` cache entry to save the
503 directory where ``LLVMConfig.cmake`` is found or allows the user to specify the
504 directory (e.g. by passing ``-DLLVM_DIR=/usr/share/llvm/cmake`` to
505 the ``cmake`` command or by setting it directly in ``ccmake`` or ``cmake-gui``).
507 This file is available in two different locations.
509 * ``<INSTALL_PREFIX>/share/llvm/cmake/LLVMConfig.cmake`` where
510 ``<INSTALL_PREFIX>`` is the install prefix of an installed version of LLVM.
511 On Linux typically this is ``/usr/share/llvm/cmake/LLVMConfig.cmake``.
513 * ``<LLVM_BUILD_ROOT>/share/llvm/cmake/LLVMConfig.cmake`` where
514 ``<LLVM_BUILD_ROOT>`` is the root of the LLVM build tree. **Note: this is only
515 available when building LLVM with CMake.**
517 If LLVM is installed in your operating system's normal installation prefix (e.g.
518 on Linux this is usually ``/usr/``) ``find_package(LLVM ...)`` will
519 automatically find LLVM if it is installed correctly. If LLVM is not installed
520 or you wish to build directly against the LLVM build tree you can use
521 ``LLVM_DIR`` as previously mentioned.
523 The ``LLVMConfig.cmake`` file sets various useful variables. Notable variables
527 The path to the LLVM CMake directory (i.e. the directory containing
531 A list of preprocessor defines that should be used when building against LLVM.
533 ``LLVM_ENABLE_ASSERTIONS``
534 This is set to ON if LLVM was built with assertions, otherwise OFF.
537 This is set to ON if LLVM was built with exception handling (EH) enabled,
541 This is set to ON if LLVM was built with run time type information (RTTI),
544 ``LLVM_INCLUDE_DIRS``
545 A list of include paths to directories containing LLVM header files.
547 ``LLVM_PACKAGE_VERSION``
548 The LLVM version. This string can be used with CMake conditionals, e.g., ``if
549 (${LLVM_PACKAGE_VERSION} VERSION_LESS "3.5")``.
551 ``LLVM_TOOLS_BINARY_DIR``
552 The path to the directory containing the LLVM tools (e.g. ``llvm-as``).
554 Notice that in the above example we link ``simple-tool`` against several LLVM
555 libraries. The list of libraries is determined by using the
556 ``llvm_map_components_to_libnames()`` CMake function. For a list of available
557 components look at the output of running ``llvm-config --components``.
559 Note that for LLVM < 3.5 ``llvm_map_components_to_libraries()`` was
560 used instead of ``llvm_map_components_to_libnames()``. This is now deprecated
561 and will be removed in a future version of LLVM.
563 .. _cmake-out-of-source-pass:
565 Developing LLVM passes out of source
566 ------------------------------------
568 It is possible to develop LLVM passes out of LLVM's source tree (i.e. against an
569 installed or built LLVM). An example of a project layout is provided below.
582 Contents of ``<project dir>/CMakeLists.txt``:
584 .. code-block:: cmake
586 find_package(LLVM REQUIRED CONFIG)
588 add_definitions(${LLVM_DEFINITIONS})
589 include_directories(${LLVM_INCLUDE_DIRS})
591 add_subdirectory(<pass name>)
593 Contents of ``<project dir>/<pass name>/CMakeLists.txt``:
595 .. code-block:: cmake
597 add_library(LLVMPassname MODULE Pass.cpp)
599 Note if you intend for this pass to be merged into the LLVM source tree at some
600 point in the future it might make more sense to use LLVM's internal
601 ``add_llvm_loadable_module`` function instead by...
604 Adding the following to ``<project dir>/CMakeLists.txt`` (after
605 ``find_package(LLVM ...)``)
607 .. code-block:: cmake
609 list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_DIR}")
612 And then changing ``<project dir>/<pass name>/CMakeLists.txt`` to
614 .. code-block:: cmake
616 add_llvm_loadable_module(LLVMPassname
620 When you are done developing your pass, you may wish to integrate it
621 into the LLVM source tree. You can achieve it in two easy steps:
623 #. Copying ``<pass name>`` folder into ``<LLVM root>/lib/Transform`` directory.
625 #. Adding ``add_subdirectory(<pass name>)`` line into
626 ``<LLVM root>/lib/Transform/CMakeLists.txt``.
628 Compiler/Platform-specific topics
629 =================================
631 Notes for specific compilers and/or platforms.
636 **LLVM_COMPILER_JOBS**:STRING
637 Specifies the maximum number of parallel compiler jobs to use per project
638 when building with msbuild or Visual Studio. Only supported for the Visual
639 Studio 2010 CMake generator. 0 means use all processors. Default is 0.