Support building with -Werror=strict-prototypes / -Werror=old-style-definition

Unfortunately "-std=c99" is not sufficient to make gcc ignore code that
uses constructs of earlier C standards, which were abandoned in C99.

See https://lwn.net/ml/fedora-devel/Y1kvF35WozzGBpc8@redhat.com/ for
some related discussion.

Change-Id: I84fd99442d0cc400fa562fa33623c142649230e2
diff --git a/tests/tdef/tdef_vty_config_subnode_test.c b/tests/tdef/tdef_vty_config_subnode_test.c
index 90c7968..d4abe09 100644
--- a/tests/tdef/tdef_vty_config_subnode_test.c
+++ b/tests/tdef/tdef_vty_config_subnode_test.c
@@ -102,7 +102,7 @@
 	return CMD_SUCCESS;
 }
 
-static void gsmnet_init_vty()
+static void gsmnet_init_vty(void)
 {
 	install_node(&gsmnet_node, config_write_gsmnet);
 	install_element(CONFIG_NODE, &cfg_net_cmd);
@@ -116,7 +116,7 @@
 
 void *root_ctx = NULL;
 
-static void print_help()
+static void print_help(void)
 {
 	printf( "options:\n"
 		"  -h	--help		this text\n"