Kill the LLVM global lock.

This patch removes the LLVM global lock, and updates all existing
users of the global lock to use their own mutex.    None of the
existing users of the global lock were protecting code that was
mutually exclusive with any of the other users of the global
lock, so its purpose was not being met.

Reviewed by: rnk

Differential Revision: http://reviews.llvm.org/D4142