[PowerPC] Support lmw/stmw in the asm parser

This adds support for the load/store multiple instructions,
currently used by the asm parser only.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185564 91177308-0d34-0410-b5e6-96231b3b80d8
Use an RWMutex instead of a Mutex in PassRegistry.
Patch by Alex Crichton <alex@crichton.co>.  Approved by Chris Lattner.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185566 91177308-0d34-0410-b5e6-96231b3b80d8