[Bug libstdc++/125890] allocator_traits<polymorphic_allocator> doesn't provide allocate_at_least in 16.1

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125890

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
I doubt that can be backported.