[Bug c/96460] Warn about signed modulo that is converted to unsigned value

[fw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96460

--- Comment #4 from Florian Weimer <fw at gcc dot gnu.org> ---
(In reply to Eric Gallager from comment #3)
> There already is a warning from -Wsign-conversion for it:

It's for the conversion, not the modulo. My hypothesis is that for the modulo,
the warning is much more helpful and can perhaps even enabled by -Wall.