* If compiling on X86 or Sparc, automagically enable the JIT for that arch

* If compiling on X86 or Sparc, automagically enable the JIT for that arch
* Setting ENABLE_X86_JIT or ENABLE_SPARC_JIT on the `make' command-line will
  force the inclusion of that JIT on a different architecture
* If neither JIT is enabled (e.g., compiling on a different architecture), the
  -march option will not be available to LLI.
* As a side effect of the $ARCH variable, the Sparc LLI can now link just a bit
  faster by not including the x86 library.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7070 91177308-0d34-0410-b5e6-96231b3b80d8