[Bug libstdc++/117214] chrono format error for time point using %c: D_T_FMT cannot be directly used as chrono-specs

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117214

--- Comment #11 from Jonathan Wakely <redi at gcc dot gnu.org> ---
The last patch cannot be backported to gcc-15 without the series of patches for
PR110739 which are too invasive to backport.

The _M_a_A, _M_b_B and _M_p functions could be rewritten on the branch to use
_M_locale_fmt but it would be a new patch, not a backport.