libstdc++: Do not use _GLIBCXX_MAKE_MOVE_ITERATOR for C++17

libstdc++: Do not use _GLIBCXX_MAKE_MOVE_ITERATOR for C++17

The _GLIBCXX_MAKE_MOVE_ITERATOR macro is needed for code that needs to
compile as C++98, where it just produces the original iterator. In
std::uninitialized_move and std::uninitialized_move_n we can just call
std::make_move_iterator directly.

libstdc++-v3/ChangeLog:

	* include/bits/stl_uninitialized.h (uninitialized_move)
	(uninitialized_move_n): Replace _GLIBCXX_MAKE_MOVE_ITERATOR with
	std::make_move_iterator.

Reviewed-by: Patrick Palka <ppalka@redhat.com>