[Bug libstdc++/120548] std::format confuses a negative sign for a thousands digit when formatting floating point numbers

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120548

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk, backports needed too.