On Sat, 15 Oct 2022 at 21:26, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> libstdc++-v3/ChangeLog:
>
>         * include/bits/charconv.h (__to_chars_10_impl): Add constexpr
>         for C++23. Remove 'static' from array.
>         * include/std/charconv (__cpp_lib_constexpr_charconv): Define.

I managed to define the feature test macro with the wrong value. Fixed
by the attached patch, pushed to trunk.