tests: fix warnings

While I don't see -Werror being used on tests anytime soon, there's no
reason to keep the warnings in tests unfixed.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/tests/test-sig.c b/tests/test-sig.c
index 7415d7a..f24da96 100644
--- a/tests/test-sig.c
+++ b/tests/test-sig.c
@@ -22,19 +22,19 @@
 #include "lib/log.h"
 #include "lib/memory.h"
 
-void
+static void
 sighup (void)
 {
   printf ("processed hup\n");
 }
 
-void
+static void
 sigusr1 (void)
 {
   printf ("processed usr1\n");
 }
 
-void
+static void
 sigusr2 (void)
 {
   printf ("processed usr2\n");