Implement P1286R2, Contra CWG1778

Implement P1286R2, Contra CWG1778

The C++11 requirement that an explicit exception-specification on a
defaulted function match the implicit one was found to be problematic for
std::atomic.  This paper, adopted in February, simply removes that
requirement: if an explicitly defaulted function has a different
exception-specification, that now works just like a user-written function:
either it isn't noexcept when it could be, or it is noexcept and will call
terminate if an exception is thrown.

	* method.c (defaulted_late_check): Don't check explicit
	exception-specification on defaulted function.
	(after_nsdmi_defaulted_late_checks): Remove.
	* parser.h (struct cp_unparsed_functions_entry): Remove classes.
	* parser.c (unparsed_classes): Remove.
	(push_unparsed_function_queues, cp_parser_class_specifier_1):
	Adjust.

From-SVN: r277351