libstdc++: Use consteval for _S_noexcept() helper functions

libstdc++: Use consteval for _S_noexcept() helper functions

These _S_noexcept() functions are only used in noexcept-specifiers and
never need to be called at runtime. They can be immediate functions,
i.e. consteval.

libstdc++-v3/ChangeLog:

	* include/bits/iterator_concepts.h (_IterMove::_S_noexcept)
	(_IterSwap::_S_noexcept): Change constexpr to consteval.
	* include/bits/ranges_base.h (_Begin::_S_noexcept)
	(_End::_S_noexcept, _RBegin::_S_noexcept, _REnd::_S_noexcept)
	(_Size::_S_noexcept, _Empty::_S_noexcept, _Data::_S_noexcept):
	Likewise.
	* include/std/concepts (_Swap::_S_noexcept): Likewise.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>