Permit -Wswitch coverage for enumerations.

Thanks to David Blakie and Richard Smith for pointing out that we can retain the
-Wswitch coverage while avoiding the warning from GCC by pushing the unreachable
outside of the switch!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210812 91177308-0d34-0410-b5e6-96231b3b80d8
MS ABI: Fix forming pointers to members of a base class

Previously we would calculate the inheritance model of a class when
requiring a pointer to member type of that class to be complete.  The
inheritance model is used to figure out how many fields are used by the
member pointer.

However, once we require a pointer to member of a derived class type to
be complete, we can form pointers to members of bases without
calculating the inheritance model for those bases.  This was causing
crashes on this simple test case:

  struct A {
    void f();
    void f(int);
  };
  struct B : public A {};
  void g() { void (B::*a)() = &B::f; }

Now we calculate the inheritance models of all base classes when
completing a member pointer type.

Fixes PR2007.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210813 91177308-0d34-0410-b5e6-96231b3b80d8