c++: alias template with dependent attributes [PR115897]

c++: alias template with dependent attributes [PR115897]

Here we're prematurely stripping the dependent alias template-id A<T> to
its defining-type-id T when used as a template argument, which in turn
causes us to essentially ignore A's vector_size attribute in the outer
template-id.

This has always been a problem for class template-ids it seems, and after
r14-2170 variable template-ids are affected as well.

This patch marks alias templates that have a dependent attribute as
complex (as with e.g. constrained alias templates) so that we don't look
through them prematurely.

	PR c++/115897

gcc/cp/ChangeLog:

	* pt.cc (complex_alias_template_p): Return true for an alias
	template with attributes.
	(get_underlying_template): Don't look through an alias template
	with attributes.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/alias-decl-77.C: New test.

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