name-lookup.c (do_nonmember_using_decl): Print an error for ambiguous type lookups.

name-lookup.c (do_nonmember_using_decl): Print an error for ambiguous type lookups.

	gcc/cp/
	* name-lookup.c (do_nonmember_using_decl): Print an error for ambiguous
	type lookups.
	(ambiguous_decl): Construct tree of ambiguous types.  Remove extaneous
	function parameter.
	(unqualified_namespace_lookup): Fix ambiguous_decl call.
	(lookup_using_namespace): Fix ambiguous_decl call.
	(qualified_lookup_using_namespace): Fix ambiguous_decl call.

	gcc/testsuite/
	* g++.dg/lookup/using18.C: New test.

From-SVN: r127347