Flush all output streams before aborting

Maybe the stdout buffer still contains something interesting that
should be flushed.

* src/emacs-module.c (module_abort): Flush all output streams before
aborting.

src/emacs-module.c

@@ -1187,7 +1187,7 @@ module_abort (const char *format, ...)
   vfprintf (stderr, format, args);
   va_end (args);
   putc ('\n', stderr);
-  fflush (stderr);
+  fflush (NULL);
   emacs_abort ();
 }