Don't reinstall sig handler if POSIX_SIGNALS.
extern int select_alarmed;
#endif
-#ifdef USG
+#if defined(USG) && !defined(POSIX_SIGNALS)
/* USG systems forget handlers when they are used;
must reestablish each time */
signal (signo, input_available_signal);
/* Must preserve main program's value of errno. */
int old_errno = errno;
-#ifdef USG
+#if defined(USG) && !defined(POSIX_SIGNALS)
if (!read_socket_hook && NILP (Vwindow_system))
{
/* USG systems forget handlers when they are used;