Support non-type constrained-type-specifiers.

	Support non-type constrained-type-specifiers.
	* parser.c (check_type_concept): Remove.
	(cp_parser_maybe_constrained_type_specifier): Don't call it.
	(synthesize_implicit_template_parm): Handle non-type and template
	template parameters.  Also compare extra args.  Return the decl.
	(cp_parser_template_argument): Handle constrained-type-specifiers for
	non-type template parameters.
	(finish_constrained_template_template_parm): Split out from
	cp_parser_constrained_template_template_parm.
	(cp_parser_nonclass_name): Move some logic into
	cp_parser_maybe_concept_name.
	(cp_parser_init_declarator): Fix error recovery.
	(get_concept_from_constraint): Remove.
	(cp_parser_simple_type_specifier): Adjust for
	synthesize_implicit_template_parm returning the decl.
	* constraint.cc (placeholder_extract_concept_and_args)
	(equivalent_placeholder_constraints): Also handle TYPE_DECL
	constrained parms.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@229860 138bc75d-0d04-0410-961f-82ee72b054a4