C2x features status

[Florian Weimer]

* Arsen Arsenović:

> On Friday, 21 October 2022 21:14:54 CEST Marek Polacek via Gcc wrote:
>> commit 0a91bdaf177409a2a5e7895bce4f0e7091b4b3ca
>> Author: Joseph Myers <joseph@codesourcery.com>
>> Date:   Wed Sep 7 13:56:25 2022 +0000
>> 
>>     c: New C2x keywords
>> 
>> which says:
>> 
>>     As with the removal of unprototyped functions, this change has a
>> high risk of breaking some old code and people doing GNU/Linux
>> distribution builds may wish to see how much is broken in a build
>> with a -std=gnu2x default.
>
> It already does break a lot.  See https://bugs.gentoo.org/870412 
> (comments go over the details).  I was intending on giving this issue a 
> proper look in the GNU toolchain frame of reference, but never got 
> around to it (and I kinda knocked priority down after managing to 
> configure properly once IIRC).

That's the implicit function declaration/implicit int change.  This
won't happen in GCC 13, it's too late for that.  I tried to make this
change a couple of years in Fedora, and just flipping the compiler flag
Does Not Work.  I hope to get there in time for GCC 14.

Thank you for sharing the Gentoo tracker.  Maybe we can reuse some
patches from there and contribute ours.  I trust Gentoo aims to upstream
patches as they become available?  Unfortunately, I expect that a lot of
these issues will be in packages that don't have an active upstream
anymore, which makes sharing patches more challenging.  In other cases,
we'll just build with -std=gnu89 (e.g. unzip
<https://bugzilla.redhat.com/show_bug.cgi?id=1750694>, it has
configure-style checking implemented without autoconf).

Thanks,
Florian