Add std::apply for C++17

Add std::apply for C++17

	* doc/xml/manual/status_cxx2017.xml: Add missing LFTSv2 features.
	* doc/html/manual/status.html: Regenerate.
	* include/Makefile.am: Add new header.
	* include/Makefile.in: Regenerate.
	* include/bits/invoke.h: New header.
	(__invoke): Make constexpr. Add && to types in exception specification.
	* include/experimental/tuple (apply, __apply_impl): Fix non-reserved
	names. Include <bits/invoke.h> and use std::__invoke.
	* include/std/functional (__invfwd, __invoke_impl, __invoke): Move to
	new header.
	(invoke): Add && to types in exception specification.
	* include/std/tuple (apply, __apply_impl): Define for C++17.
	* testsuite/20_util/tuple/apply/1.cc: New test.
	* testsuite/20_util/tuple/element_access/get_neg.cc: Adjust dg-error
	lineno.

From-SVN: r239183