[Bug libstdc++/96942] std::pmr::monotonic_buffer_resource causes CPU cache misses

[amonakov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96942

--- Comment #20 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
Round up to 64 bytes (typical cache line size).