c++: maybe_dependent_member_ref and typenames [PR118626]

c++: maybe_dependent_member_ref and typenames [PR118626]

Here during maybe_dependent_member_ref for accepted_type<_Up>, we
correctly don't strip the typedef because it's a complex one (its
defaulted template parameter isn't used in its definition) and so
we recurse to consider its corresponding TYPE_DECL.

We then incorrectly decide to not rewrite this use because of the
TYPENAME_TYPE shortcut.  But I don't think this shortcut should apply to
a typedef TYPE_DECL.

	PR c++/118626

gcc/cp/ChangeLog:

	* pt.cc (maybe_dependent_member_ref): Restrict TYPENAME_TYPE
	shortcut to non-typedef TYPE_DECL.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/class-deduction-alias25a.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>