[Bug other/92435] % format codes for diagnostics are not documented in the GCC internals manual

[egallager at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92435

--- Comment #4 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #3)
> See also the following question:
>   https://gcc.gnu.org/pipermail/gcc/2021-September/237281.html
> It would be helpful to document the GCC specific directives somewhere.  The
> -Wformat-diag GCC-developer warning option could also stand to be documented.

Yeah I was trying to convince the Wesnoth devs to look at -Wformat-diag for
inspiration for their own message-strings linter, but since it wasn't
documented, they didn't really know what to do, so I agree that documenting
that would be useful, too