PR c++/41305, DR 384
* name-lookup.c (arg_assoc_class): Split out arg_assoc_class_only
and arg_assoc_bases.
(friend_of_associated_class_p): Remove.
(arg_assoc_namespace): Don't call it.
(arg_assoc_template_arg): Use arg_assoc_class_only for member
template context.
(arg_assoc_type): Handle UNION_TYPE and ENUMERAL_TYPE properly.