[MS ABI] Pick an inheritance model if we resolve an overload set

We didn't assign an inheritance model for 'Foo' if the event an
exrepssion like '&Foo::Bar' occured if 'Bar' could resolve to multiple
functions.

Once the overload set is resolved to a particular member, we enforce a
specific inheritance model.

This fixes PR28360.

llvm-svn: 274202