mark unused parameters in signal handlers

Signal handlers receive their signal number as a parameter, but many
don't care what it is (because they only handle one signal, or because
their action is the same regardless of the signal). Mark such parameters
to silence -Wunused-parameter.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

progress.c

@@ -59,7 +59,7 @@ void progress_test_force_update(void)
 }
 
 
-static void progress_interval(int signum)
+static void progress_interval(int signum UNUSED)
 {
 	progress_update = 1;
 }