PR libstdc++/66693.

	* include/std/tuple (tuple_element, tuple_size, tuple_element_t,
	__tuple_element_t): Move to...
	* include/std/utility: ...here.
	* testsuite/20_util/pair/astuple/astuple.cc: Adjust.
	* testsuite/20_util/pair/astuple/astuple_cpp14.cc: New.
	* testsuite/20_util/tuple/tuple_element.cc: Adjust.
	* testsuite/20_util/tuple/tuple_element_t.cc: Likewise.
	* testsuite/20_util/tuple/tuple_size.cc: Likewise.
	* testsuite/23_containers/array/tuple_interface/tuple_element.cc:
	Likewise.
	* testsuite/23_containers/array/tuple_interface/tuple_element_cpp14.cc:
	New.
	* testsuite/23_containers/array/tuple_interface/tuple_size.cc: Adjust.

From-SVN: r231875