[C++ PATCH] Merge some using-decl handling

[C++ PATCH] Merge some using-decl handling

https://gcc.gnu.org/ml/gcc-patches/2019-11/msg00971.html
	gcc/cp/
	* name-lookup.c (lookup_using_decl): New function, merged from ...
	(do_class_using_decl): ... here.  Call it.  And ...
	(finish_nonmember_using_decl): ... here.  Call it.

	gcc/testsuite/
	* g++.dg/cpp0x/using-enum-2.C: Adjust expected error text.
	* g++.dg/cpp0x/using-enum-3.C: Likewise.
	* g++.dg/lookup/using4.C: Likewise.
	* g++.dg/lookup/using7.C: Likewise.
	* g++.dg/template/using12.C: Likewise.
	* g++.dg/template/using18.C: Likewise.
	* g++.dg/template/using22.C: Likewise.

From-SVN: r278106