This refactoring reduces the memory usage and compilation time to parse
a number of headers that depend on std::pair, std::tuple or std::array.
Previously the headers for these class templates were all intertwined,
due to the common dependency on std::tuple_size, std::tuple_element and
their std::get overloads. This decouples the headers by moving some
parts of <utility> into a new <bits/utility.h> header. This means that
<array> and <tuple> no longer need to include the whole of <utility>,
and <tuple> no longer needs to include <array>.

This decoupling benefits headers such as <thread> and <scoped_allocator>
which only need std::tuple, and so no longer have to parse std::array.

Some other headers such as <any>, <optional> and <variant> no longer
need to include <utility> just for the std::in_place tag types, so
do not have to parse the std::pair definitions.

Removing direct uses of <utility> also means that the std::rel_ops
namespace is not transitively declared by other headers.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/Makefile.am: Add bits/utility.h header.
	* include/Makefile.in: Regenerate.
	* include/bits/utility.h: New file.
	* include/std/utility (tuple_size, tuple_element): Move
	to new header.
	* include/std/type_traits (__is_tuple_like_impl<tuple<T...>>):
	Move to <tuple>.
	(_Index_tuple, _Build_index_tuple, integer_sequence): Likewise.
	(in_place_t, in_place_index_t, in_place_type_t): Likewise.
	* include/bits/ranges_util.h: Include new header instead of
	<utility>.
	* include/bits/stl_pair.h (tuple_size, tuple_element): Move
	partial specializations for std::pair here.
	(get): Move overloads for std::pair here.
	* include/std/any: Include new header instead of <utility>.
	* include/std/array: Likewise.
	* include/std/memory_resource: Likewise.
	* include/std/optional: Likewise.
	* include/std/variant: Likewise.
	* include/std/tuple: Likewise.
	(__is_tuple_like_impl<tuple<T...>>): Move here.
	(get) Declare overloads for std::array.
	* include/std/version (__cpp_lib_tuples_by_type): Change type
	to long.
	* testsuite/20_util/optional/84601.cc: Include <utility>.
	* testsuite/20_util/specialized_algorithms/uninitialized_fill/constrained.cc:
	Likewise.
	* testsuite/23_containers/array/tuple_interface/get_neg.cc:
	Adjust dg-error line numbers.
	* testsuite/std/ranges/access/cbegin.cc: Include <utility>.
	* testsuite/std/ranges/access/cend.cc: Likewise.
	* testsuite/std/ranges/access/end.cc: Likewise.
	* testsuite/std/ranges/single_view.cc: Likewise.

Tested powerpc64le-linux. Committed to trunk.