Allow lookup into dependent bases in more places under -fms-compatibility

We currently allow unqualified lookup for instance methods but not
static methods because we can't recover with a semantic 'this->'
insertion.

ATL headers have static methods that do unqualified lookup into
dependent base classes.  The pattern looks like:

  template <typename T> struct Foo : T {
    static int *getBarFromT() { return Bar; }
  };

Now we recover as if the user had written:

  template <typename T> struct Foo : T {
    static int *getBarFromT() { return Foo::Bar; }
  };

... which will eventually look up Bar in T at instantiation time.

Now we emit a diagnostic in both cases, and delay lookup in other
contexts where 'this' is available and refers to a class with dependent
bases.

Reviewed by: rsmith

Differential Revision: http://reviews.llvm.org/D4079