[Bug libstdc++/121148] Should use modular arithmetic for _Atomic_word

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121148

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> ---
OK great, thanks all.

I have a patch ready that flips the non-inline atomics to use -fwrapv and fixes
the handful of inline ones to avoid signed overflow.