[RFC] posix: Make system, popen, and wordexp try pidfd_spawn first (BZ 34001)

[Florian Weimer]

* Adhemerval Zanella Netto:

> On 05/05/26 10:05, Cristian Rodríguez wrote:
>> On Mon, May 4, 2026 at 9:58 AM Adhemerval Zanella Netto
>> <adhemerval.zanella@linaro.org> wrote:
>>  (afaik waitid (PIDFD, ...) will signal an error if the process is
>>> already reaped).
>> 
>> Yes, it will return ECHILD..afaik.
>
> And I am not sure we can change it, because it will subtly change the
> functions semantics and we will always need a clone fallback (that
> always send the signal) for ABI that do not have clone3 and on kernel
> that do not support it.

I think we could perhaps hide the process launch for wordexp, but not
for system and popen.  For system and popen, some applications expect to
see signals.

Thanks,
Florian