Teach Clang about the PPC64 memory sanitizer implementation.

Summary:
This is the Clang part of the PPC64 memory sanitizer implementation in
D10648.

Reviewers: kcc, eugenis, willschm, wschmidt, samsonov

Reviewed By: samsonov

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D10650

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@240628 91177308-0d34-0410-b5e6-96231b3b80d8