c++: alias with same name as base fn [PR91706]

c++: alias with same name as base fn [PR91706]

This is a bit complex.  Looking up c<T> in the definition of D::c finds
C::c, OK.  Looking up c in the definition of E finds D::c, OK.  Since the
alias is not dependent, we strip it from the template argument, leaving

using E = A<decltype(c<T>())>;

where 'c' still refers to C::c.  But instantiating E looks up 'c' again and
finds D::c, which isn't a function, and sadness ensues.

I think the bug here is looking up 'c' in D at instantiation time; the
declaration we found before is not dependent.  This seems to happen because
baselink_for_fns gets BASELINK_BINFO wrong; it is supposed to be the base
where lookup found the functions, C in this case.

gcc/cp/ChangeLog:

	PR c++/91706
	* semantics.c (baselink_for_fns): Fix BASELINK_BINFO.

gcc/testsuite/ChangeLog:

	PR c++/91706
	* g++.dg/template/lookup17.C: New test.