libstdc++: Fix some C++20 algorithms to work in parallel mode

libstdc++: Fix some C++20 algorithms to work in parallel mode

Some new algorithms need to use _GLIBCXX_STD_A to refer to the "normal"
version of the algorithm, to workaround the namespace dance done for
parallel mode.

	PR libstdc++/94971 (partial)
	* include/bits/ranges_algo.h (ranges::__sample_fn): Qualify
	std::sample using macro to work in parallel mode.
	(__sort_fn): Likewise for std::sort.
	(ranges::__nth_element_fn): Likewise for std::nth_element.
	* include/bits/stl_algobase.h (lexicographical_compare_three_way):
	Likewise for std::__min_cmp.
	* include/parallel/algobase.h (lexicographical_compare_three_way):
	Add to namespace std::__parallel.