Teach LLVM about the PPC64 memory sanitizer implementation.

Summary:
This is the LLVM part of the PPC memory sanitizer implementation in
D10648.

Reviewers: kcc, samsonov, willschm, wschmidt, eugenis

Reviewed By: eugenis

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10649

llvm-svn: 240627