Add a test for MS-ABI this adjustment for virtual calls to member operators.

They too were fixed by r223185, despite the commit message saying otherwise.
Add a test that makes sure they don't regress.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@223714 91177308-0d34-0410-b5e6-96231b3b80d8