[MSan] [MIPS] Adding support for MIPS64 (patch by Mohit Bhakkad).

Reviewed at http://reviews.llvm.org/D5906


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@222388 91177308-0d34-0410-b5e6-96231b3b80d8