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.
llvm-svn: 23003
f85fabeb71