P0604R0 add invoke_result, is_invocable etc. for C++17

P0604R0 add invoke_result, is_invocable etc. for C++17

	* include/bits/invoke.h (__invoke): Use __invoke_result instead of
	result_of, and __is_nothrow_invocable instead of
	__is_nothrow_callable.
	* include/bits/shared_ptr_base.h (__shared_ptr): Use __is_invocable
	instead of __is_callable.
	* include/std/functional (invoke): use invoke_result_t instead of
	result_of_t and is_nothrow_invocable instead of is_nothrow_callable.
	(_Not_fn): Use __invoke_result instead of result_of.
	* include/std/type_traits (__result_of_memobj, __result_of_memfun):
	Remove partial specializations for reference_wrapper types.
	(__result_of_impl): Use __inv_unwrap to strip reference_wrapper.
	(__invoke_result): Define replacement for result_of and then use it to
	define result_of.
	(__is_callable_impl, __is_callable, __is_nothrow_callable): Replace
	with __is_invocable_impl, __is_invocable, and __is_nothrow_invocable
	respectively.
	(invoke_result, invoke_result_t): Define for C++17.
	(is_callable, is_nothrow_callable): Replace with is_invocable,
	is_invocable_r, is_nothrow_invocable, and is_nothrow_invocable_r.
	(is_callable_v, is_nothrow_callable_v): Replace with is_invocable_v,
	is_invocable_r_v, is_nothrow_invocable_v, and is_nothrow_invocable_r_v.
	* include/std/variant (hash<variant<T...>>): Use is_nothrow_invocable_v
	instead of is_nothrow_callable_v.
	* testsuite/20_util/function_objects/invoke/59768.cc: Remove unused
	main function.
	* testsuite/20_util/function_objects/not_fn/1.cc: Use is_invocable
	instead of is_callable.
	* testsuite/20_util/is_callable/*: Rename directory and adjust tests
	to use new traits.
	* testsuite/20_util/is_notjrow_callable/*: Likewise.
	* testsuite/20_util/optional/hash.cc: Use is_invocable_v instead of
	is_callable.
	* testsuite/20_util/variant/hash.cc: Likewise.

From-SVN: r246036