[msan] MSanDR: initial commit.

MSanDR is a DynamoRio-based tool that handles uninstrumented libraries and
dynamically generated code for MSan.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@175883 91177308-0d34-0410-b5e6-96231b3b80d8