libstdc++-v3/ChangeLog:

	* include/std/variant (__variant::__get(in_place_index_t<N>, U&&)):
	Rename to __get_n and remove first argument. Replace pair of
	overloads with a single function using 'if constexpr'.
	(__variant::__get(Variant&&)): Adjust to use __get_n.

Tested powerpc64le-linux. Committed to trunk.