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: I98a3c0d5cfda2c4b020652efb4f445f8288342b6
diff --git a/tests/mgcp_client/mgcp_client_test.c b/tests/mgcp_client/mgcp_client_test.c
index 9f09a99..ef05adc 100644
--- a/tests/mgcp_client/mgcp_client_test.c
+++ b/tests/mgcp_client/mgcp_client_test.c
@@ -315,7 +315,7 @@
 	msgb_free(msg);
 }
 
-void test_mgcp_client_cancel()
+void test_mgcp_client_cancel(void)
 {
 	mgcp_trans_id_t trans_id;
 	struct msgb *msg;
@@ -487,7 +487,7 @@
 	},
 };
 
-void test_sdp_section_start()
+void test_sdp_section_start(void)
 {
 	int i;
 	int failures = 0;