[Bug libstdc++/120650] Error of requesting %d from month_day_last is not detected at compile time

[tkaminsk at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120650

--- Comment #2 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
I think we may want to backport it, so I should land to separate fix, before
rework to use type erasing.