Don't use printf %n.

Index: src/emacs.c
--- src/emacs.c.orig
+++ src/emacs.c
@@ -2958,25 +2958,17 @@ shut_down_emacs (int sig, Lisp_Object stuff)
       reset_all_sys_modes ();
       if (sig && sig != SIGTERM)
 	{
-	  static char const fmt[] = "Fatal error %d: %n%s\n";
+	  static char const fmt[] = "Fatal error %d: ";
 #ifdef HAVE_HAIKU
 	  if (haiku_debug_on_fatal_error)
 	    debugger ("Fatal error in Emacs");
 #endif
-	  char buf[max ((sizeof fmt - sizeof "%d%n%s\n"
-			 + INT_STRLEN_BOUND (int) + 1),
-			min (PIPE_BUF, MAX_ALLOCA))];
+	  char buf[sizeof fmt - strlen ("%d") + INT_STRLEN_BOUND (int) + 1];
 	  char const *sig_desc = safe_strsignal (sig);
-	  int nlen;
-	  int buflen = snprintf (buf, sizeof buf, fmt, sig, &nlen, sig_desc);
-	  if (0 <= buflen && buflen < sizeof buf)
-	    emacs_write (STDERR_FILENO, buf, buflen);
-	  else
-	    {
-	      emacs_write (STDERR_FILENO, buf, nlen);
-	      emacs_write (STDERR_FILENO, sig_desc, strlen (sig_desc));
-	      emacs_write (STDERR_FILENO, fmt + sizeof fmt - 2, 1);
-	    }
+	  snprintf (buf, sizeof buf, fmt, sig);
+	  emacs_write (STDERR_FILENO, buf, strlen (buf));
+	  emacs_write (STDERR_FILENO, sig_desc, strlen (sig_desc));
+	  emacs_write (STDERR_FILENO, "\n", 1);
 	}
     }
 #else