libstdc++: Add always_inline to casting/forwarding functions in bits/move.h

libstdc++-v3/ChangeLog:

	* include/bits/move.h (__addressof, forward, forward_like, move)
	(move_if_noexcept, addressof): Add always_inline attribute.
	Replace _GLIBCXX_NODISCARD with [[__nodiscard__]].