c++: member vs global template [PR106310]

For backward compatibility we still want to allow patterns like
this->A<T>::foo, but the template keyword in a qualified name is
specifically to specify that a dependent name is a template, so don't look
in the enclosing scope at all.

Also fix handling of dependent bases: if member lookup in the current
instantiation fails and we have dependent bases, the lookup is dependent.
We were already handling that for the case where lookup in the enclosing
scope also fails, but we also want it to affect that lookup itself.

	PR c++/106310

gcc/cp/ChangeLog:

	* parser.cc (cp_parser_template_name): Skip non-member
	lookup after the template keyword.
	(cp_parser_lookup_name): Pass down template_keyword_p.

gcc/testsuite/ChangeLog:

	* g++.dg/template/template-keyword4.C: New test.