* include/std/bit (__cpp_lib_bitops): Define.
	* include/std/version (__cpp_lib_constexpr): Remove.
	(__cpp_lib_bitops, __cpp_lib_constexpr_dynamic_alloc): Define.
	* testsuite/26_numerics/bit/header.cc: New test.
	* testsuite/26_numerics/bit/header-2.cc: New test.
	* testsuite/20_util/allocator_traits/header.cc: New test.
	* testsuite/20_util/allocator_traits/header-2.cc: New test.

From-SVN: r277633