[msan] Add a test for vector compare x86 intrinsics.

This was actually meant to go in with r267966, but I forgot to
git add the file. Better late than never.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@270515 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed