For PR616:

For PR616:
These patches make threading optional in LLVM. The configuration scripts are now
modified to accept a --disable-threads switch. If this is used, the Mutex class
will be implemented with all functions as no-op. Furthermore, linking against
libpthread will not be done. Finally, the ParallelJIT example needs libpthread
so its makefile was changed to always add -lpthread to the link line.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23003 91177308-0d34-0410-b5e6-96231b3b80d8