Remove Concepts from -std=c++1z.

Remove Concepts from -std=c++1z.

gcc/c-family/
	* c-opts.c (set_std_cxx1z): Don't enable concepts.
gcc/testsuite/
	* lib/g++-dg.exp (g++-dg-runtest): Handle "concepts" in std list.
	* lib/target-supports.exp (check_effective_target_concepts): New.
gcc/cp/
	* parser.c (cp_parser_diagnose_invalid_type_name): Give helpful
	diagnostic for use of "concept".
	(cp_parser_requires_clause_opt): And "requires".
	(cp_parser_type_parameter, cp_parser_late_return_type_opt)
	(cp_parser_explicit_template_declaration): Adjust.
	* Make-lang.in (check-c++-all): Add "concepts" to std list.

From-SVN: r234069