Add test case for commit r178031.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178038 91177308-0d34-0410-b5e6-96231b3b80d8
Add PREFETCHW codegen support

- Add 'PRFCHW' feature defined in AVX2 ISA extension



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178040 91177308-0d34-0410-b5e6-96231b3b80d8