bug#47596: File descriptor error when exiting emacs on android 11

[Henrik Grimler <henrik@grimler.se>]

Hi Lars,

On Thu, 2021-05-06 at 12:45 +0200, Lars Ingebrigtsen wrote:
> > I probably should have included a bit more context in the android bug
> > report to better show what the code does. 
> 
> Did you try to include this context in the Android bug report and see
> what they say then?
> 

I added another comment now with a slightly more verbose example: 

```
#include <stdlib.h>
#include <unistd.h>

/* If FD is not already open, arrange for it to be open with FLAGS.  */
static void
force_open (int fd, int flags)
{
  if (dup2 (fd, fd) < 0)
    {
      int n = open ("/dev/null", flags);
      if (n < 0 || (fd != n && (dup2 (n, fd) < 0 || close (n) == 0 !=
0)))
	exit (EXIT_FAILURE);
    }
}

/* A stream that is like stderr, except line buffered.  It is NULL
   during startup, or if line buffering is not in use.  */
static FILE *buferr;

int
main()
{
  /* Make sure stderr are open to something, so that the file
   descriptor is not hijacked by later system calls.  */
  force_open (STDERR_FILENO, O_RDONLY);

  /* Set buferr if possible on platforms defining _PC_PIPE_BUF, as
     they support the notion of atomic writes to pipes.  */
  #ifdef _PC_PIPE_BUF
    buferr = fdopen (STDERR_FILENO, "w");
    if (buferr)
      setvbuf (buferr, NULL, _IOLBF, 0);
  #endif

  int err = buferr && (fflush (buferr) != 0 || ferror (buferr));
  if (err | (fclose (stderr) != 0))
    return 1;
  return 0;
}
```

Hopefully they have time to provide some feedback.

Best regards,
Henrik Grimler