libstdc++: Harmonize <version> and other headers

libstdc++: Harmonize <version> and other headers

Due to recent, large changes in libstdc++, the feature test macros
declared in <version> got out of sync with the other headers that
possibly declare them.

libstdc++-v3/ChangeLog:

	* include/bits/unique_ptr.h (__cpp_lib_constexpr_memory):
	Synchronize the definition block with...
	* include/bits/ptr_traits.h (__cpp_lib_constexpr_memory):
	... this one here.  Also define the 202202L value, rather than
	leaving it up to purely unique_ptr.h, so that the value is
	synchronized across all headers.
	(__gnu_debug::_Safe_iterator_base): Move into new conditional
	block.
	* include/std/memory (__cpp_lib_atomic_value_initialization):
	Define on freestanding under the same conditions as in
	atomic_base.h.
	* include/std/version (__cpp_lib_robust_nonmodifying_seq_ops):
	Also define on freestanding.
	(__cpp_lib_to_chars): Ditto.
	(__cpp_lib_gcd): Ditto.
	(__cpp_lib_gcd_lcm): Ditto.
	(__cpp_lib_raw_memory_algorithms): Ditto.
	(__cpp_lib_array_constexpr): Ditto.
	(__cpp_lib_nonmember_container_access): Ditto.
	(__cpp_lib_clamp): Ditto.
	(__cpp_lib_constexpr_char_traits): Ditto.
	(__cpp_lib_constexpr_string): Ditto.
	(__cpp_lib_sample): Ditto.
	(__cpp_lib_lcm): Ditto.
	(__cpp_lib_constexpr_iterator): Ditto.
	(__cpp_lib_constexpr_char_traits): Ditto.
	(__cpp_lib_interpolate): Ditto.
	(__cpp_lib_constexpr_utility): Ditto.
	(__cpp_lib_shift): Ditto.
	(__cpp_lib_ranges): Ditto.
	(__cpp_lib_move_iterator_concept): Ditto.
	(__cpp_lib_constexpr_numeric): Ditto.
	(__cpp_lib_constexpr_functional): Ditto.
	(__cpp_lib_constexpr_algorithms): Ditto.
	(__cpp_lib_constexpr_tuple): Ditto.
	(__cpp_lib_constexpr_memory): Ditto.