c++: preserve BASELINK from lookup [PR91706]

In the earlier patch for PR91706 I fixed the BASELINK built by
baselink_for_fns, but since we already had one from lookup, we should keep
that one around instead of stripping it.  The removed hunk in
get_class_binding was a wierdly large amount of code to decide whether to
pull out BASELINK_FUNCTIONS.

gcc/cp/ChangeLog:

	PR c++/91706
	* name-lookup.c (get_class_binding): Keep a BASELINK.
	(set_inherited_value_binding_p): Adjust.
	* lambda.c (is_lambda_ignored_entity): Adjust.
	* pt.c (lookup_template_function): Copy a BASELINK before
	modifying it.