posix_spawn facility

[Bruno Haible]

Hi Corinna,

> > Would it be possible to change Cygwin's posix_spawnp implementation,
> > so that both tests succeed?
> 
> Basically, yes, but...

Thanks!

> > Disclaimer: I have done my tests with Cygwin 2.9.0; so, if things have
>                                         ^^^^^^^^^^^^
> 					2017-09-07
> 
> I'm a bit puzzled. You quote that only Cygwin 3.1.7 has the fixed
> posix_spawn, but then you test this with a version three years older?

I have now verified that the findings with Cygwin 3.4.6 are the same as
with Cygwin 2.9.0. I had expected that, based on browsing through the
Cygwin git history; I confirm it now.

Btw, there are two more functions in the posix_spawn family meanwhile:
  * posix_spawn_file_actions_addchdir_np
    implemented by glibc [1], musl libc, macOS, FreeBSD [2], Solaris ≥ 11.3
    used by a few packages (Firefox, Chromium, Rust)
  * posix_spawn_file_actions_addfchdir_np
    implemented in glibc, musl libc
    but not used by any package so far [3].

The next POSIX will contain these functions (without the _np suffix).[4]

Bruno

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=17405
[2] https://man.freebsd.org/cgi/man.cgi?query=posix_spawn_file_actions_adddup2&apropos=0&sektion=3&manpath=FreeBSD+11-current&format=html
[3] https://codesearch.debian.net/
[4] https://www.austingroupbugs.net/view.php?id=1208