Re: master 2c79a8f 2/2: Use posix_spawn if possible.

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Tue, 29 Dec 2020 17:29:59 +0100
> Cc: Emacs developers <emacs-devel@gnu.org>
> 
> (I'm still trying to set up some emulated Windows installation, but
> haven't really been successful so far.)

Thank you for your efforts.

> Gnulib provides a stub definition for posix_spawn on Windows as well
> (in fact, as of a few days ago, it provides a non-stub
> implementation), so linking shouldn't fail. Also compiling the stub
> implementation on Windows shouldn't hurt; if it's never called the
> linker will likely remove the stub.

Based on bitter experience, I doubt that, but we shall see.

> What error messages do you see on Windows when trying to build the branch?

The below is only for compiling Gnulib; the build process stopped
after that, so what will happen in lib-src/ and src/ is still TBD:

    CC       getdtablesize.o
  getdtablesize.c:58:1: warning: no previous prototype for 'getdtablesize' [-Wmissing-prototypes]
     58 | getdtablesize (void)
	| ^~~~~~~~~~~~~
    CC       open.o
  open.c: In function 'sys_open':
  open.c:131:48: error: 'O_CLOEXEC' undeclared (first use in this function)
    131 |                   flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
	|                                                ^~~~~~~~~
  open.c:131:48: note: each undeclared identifier is reported only once for each function it appears in
  Makefile:95: recipe for target `open.o' failed
  make[1]: *** [open.o] Error 1
    CC       spawn_faction_adddup2.o
  spawn_faction_adddup2.c: In function 'rpl_posix_spawn_file_actions_adddup2':
  spawn_faction_adddup2.c:26:30: warning: implicit declaration of function 'getdtablesize'; did you mean 'getpagesize'? [-Wimplicit-function-declaration]
     26 | # define __sysconf(open_max) getdtablesize ()
	|                              ^~~~~~~~~~~~~
  spawn_faction_adddup2.c:40:15: note: in expansion of macro '__sysconf'
     40 |   int maxfd = __sysconf (_SC_OPEN_MAX);
	|               ^~~~~~~~~
  spawn_faction_adddup2.c:26:30: warning: nested extern declaration of 'getdtablesize' [-Wnested-externs]
     26 | # define __sysconf(open_max) getdtablesize ()
	|                              ^~~~~~~~~~~~~
  spawn_faction_adddup2.c:40:15: note: in expansion of macro '__sysconf'
     40 |   int maxfd = __sysconf (_SC_OPEN_MAX);
	|               ^~~~~~~~~
    CC       cloexec.o
  cloexec.c: In function 'dup_cloexec':
  cloexec.c:82:10: warning: implicit declaration of function 'fcntl' [-Wimplicit-function-declaration]
     82 |   return fcntl (fd, F_DUPFD_CLOEXEC, 0);
	|          ^~~~~
  cloexec.c:82:10: warning: nested extern declaration of 'fcntl' [-Wnested-externs]
  cloexec.c:82:21: error: 'F_DUPFD_CLOEXEC' undeclared (first use in this function)
     82 |   return fcntl (fd, F_DUPFD_CLOEXEC, 0);
	|                     ^~~~~~~~~~~~~~~
  cloexec.c:82:21: note: each undeclared identifier is reported only once for each function it appears in
  cloexec.c:83:1: warning: control reaches end of non-void function [-Wreturn-type]
     83 | }
	| ^
  Makefile:95: recipe for target `cloexec.o' failed
  make[1]: *** [cloexec.o] Error 1