projects/sample: Import adapted form of current LLVM autoconf/Makefile setup so that...

projects/sample: Import adapted form of current LLVM autoconf/Makefile setup so that projects/sample is standalone and not tied to the LLVM build setup.
 - This currently just moves over all of the behavior from LLVM. Eventually all of the configure checks that are directly needed by the LLVM build setup should probably go away, and the project should manage their own configuration checks if necessary.

 - This is the 1st half of this work, the actual Makefile.common hasn't moved over yet. I've tried to stage this in such a way that incremental builds will properly reconfigure for most active developers (the Makefiles don't handle reconfiguring in a perfectly reliable way, and I haven't found an easy way to make them do so).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@142456 91177308-0d34-0410-b5e6-96231b3b80d8