[Bug libstdc++/121789] std:uninitialized_move_n() and friends don't optimize to memcpy

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121789

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The warning went away on trunk with r17-603-gacfdad706d8acc which rewrote parts
of std::vector. That means the false positive warning is probably still latent
on trunk.