How can Autoconf help with the transition to stricter compilation defaults?

[Florian Weimer via cfe-commits]

* Paul Eggert:

> On 2022-11-14 04:41, Aaron Ballman wrote:
>> it's generally a problem when autoconf relies on invalid
>> language constructs
>
> Autoconf *must* rely on invalid language constructs, if only to test
> whether the language constructs work. And Clang therefore must be 
> careful about how it diagnoses invalid constructs. Clang shouldn't
> willy-nilly change the way it reports invalid constructs, as that can 
> break Autoconf.

This is only true for the status quo.  We could finally band together
and define an interface between autoconf and the toolchain that avoids
feature probing through source code fragments for common cases.  It
might make configure scripts to run quite a bit faster, too.

That being said, system compilers need to be careful when turning
warnings into errors by default, but that doesn't mean we should never
do such changes, particularly when we know based on interactions with
programmers that the warnings are not sufficient for avoiding wasted
time.

Thanks,
Florian