c++: unifying specializations of non-primary tmpls [PR120161]

c++: unifying specializations of non-primary tmpls [PR120161]

Here unification of P=Wrap<int>::type, A=Wrap<long>::type wrongly
succeeds ever since r14-4112 which made the RECORD_TYPE case of unify
no longer recurse into template arguments for non-primary templates
(since they're a non-deduced context) and so the int/long mismatch that
makes the two types distinct goes unnoticed.

In the case of (comparing specializations of) a non-primary template,
unify should still go on to compare the types directly before returning
success.

	PR c++/120161

gcc/cp/ChangeLog:

	* pt.cc (unify) <case RECORD_TYPE>: When comparing specializations
	of a non-primary template, still perform a type comparison.

gcc/testsuite/ChangeLog:

	* g++.dg/template/unify13.C: New test.

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