Deprecate some C++ extensions

Deprecate some C++ extensions

https://gcc.gnu.org/ml/gcc-patches/2018-03/msg00995.html
	* doc/extend.texi (Deprecated Features): Update deprecared flags,
	mention anon-struct/union members and trailing attributes.

	cp/
	* class.c (finish_struct_anon_r): Refactor, deprecate anything
	other than public non-static data members.
	* parser.c (cp_parser_init_declarator): Deprecate attributes after
	parenthesized initializer.

	testsuite/
	* g++.dg/ext/anon-struct6.C: Adjust.
	* g++.dg/ext/deprecate-1.C: New.
	* g++.dg/ext/deprecate-2.C: New.
	* g++.dg/lookup/pr84602.C: Adjust.
	* g++.dg/lookup/pr84962.C: Adjust.
	* g++.old-deja/g++.other/anon4.C

From-SVN: r258712