[Bug c++/87656] Useful flags to enable with -Wall or -Wextra

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87656

--- Comment #12 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to David Binderman from comment #11)
> -Wold-style-definition
> 
> KnR style function definitions have been deprecated for about 35 years.

+1

> Yes, there is a warning for it in gcc, but that warning isn't in either
> -Wall or -Wextra. 
> 
> Also, switching on -std=c2x only makes it a warning, not an error. 
> That doesn't sound correct to me. AFAIK KnR is removed from c2x.

It can stay there as a GCC extension no problem.  If there is a warning for it
it is not a problem anymore, esp. if that warning is in -Wall or on by default
even.

The only reason to remove support for this is if it actually simplifies the
compiler code itself, which means we have to completely not support it anymore.
So let's first have a default warning, and then see if anything in the wild
still uses old-style functions defs?