c++: cv-qualified dependent name of alias tmpl [PR100592]

c++: cv-qualified dependent name of alias tmpl [PR100592]

Here, the dependent template name in the return type of f() resolves to
an alias of int& after substitution, and we end up complaining about
qualifying this reference type with 'const' from cp_build_qualified_type
rather than just silently dropping the qualification as per [dcl.ref]/1.

The problem is ultimately that make_typename_type ignores the
tf_keep_type_decl flag when the dependent name is a template-id.  This
in turn causes the TYPE_DECL check within tsubst <case TYPENAME_TYPE>
to fail, and so we end up not passing tf_ignore_bad_quals to
cp_build_qualified_type.  This patch fixes this by making
make_typename_type respect the tf_keep_type_decl flag in this situation.

	PR c++/100592

gcc/cp/ChangeLog:

	* decl.c (make_typename_type): After calling
	lookup_template_class, adjust the result to its TYPE_NAME and
	then consider the tf_keep_type_decl flag.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/alias-decl-71.C: New test.