Implement P0522R0, matching of template template arguments.

Implement P0522R0, matching of template template arguments.

gcc/c-family/
	* c.opt (-fnew-ttp-matching): New flag.
	* c-opts.c (c_common_post_options): Default on if -std=c++1z.
gcc/cp/
	* pt.c (coerce_template_template_parms): Allow a template argument
	that's less specialized than the parameter.
	(unify_bound_ttp_args): Adjust parm's args to apply to arg's
	template.
	(coerce_template_args_for_ttp): Split out from
	lookup_template_class_1.
	(coerce_ttp_args_for_tta, store_defaulted_ttp)
	(lookup_defaulted_ttp, add_defaults_to_ttp): New.
	(process_partial_specialization): Set DECL_CONTEXT of
	template template-parameters.
	(coerce_template_parms): Only inform when complain.
	(expand_template_argument_pack): Handle error_mark_node.
	(convert_template_argument, template_args_equal, unify): Handle
	any_targ_node.
	* cp-tree.h (enum cp_tree_index): Add CPTI_ANY_TARG.
	(any_targ_node): New.
	* decl.c (cxx_init_decl_processing): Set it.
	* name-lookup.c (consider_binding_level): Ignore names with embedded
	spaces.

From-SVN: r243871