MS ABI: Handle member function pointers returning a member data pointer

MSVC doesn't decide what the inheritance model for a returned member
pointer *until* a call expression returns it.

This fixes PR20017.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@215164 91177308-0d34-0410-b5e6-96231b3b80d8