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/codec/codec_ecu_fr_test.c b/tests/codec/codec_ecu_fr_test.c
index 4040ce9..a9dae89 100644
--- a/tests/codec/codec_ecu_fr_test.c
+++ b/tests/codec/codec_ecu_fr_test.c
@@ -183,7 +183,7 @@
 }
 
 /* Simulate a real life situation: voice frames with a few dropouts */
-void test_fr_concealment_realistic()
+void test_fr_concealment_realistic(void)
 {
 	struct osmo_ecu_fr_state state;
 	uint8_t frame[GSM_FR_BYTES];
@@ -219,7 +219,7 @@
 }
 
 /* Simulate a real life situation: voice frames with a few dropouts, using generic core */
-void test_fr_concealment_realistic_core()
+void test_fr_concealment_realistic_core(void)
 {
 	struct osmo_ecu_state *state = osmo_ecu_init(NULL, OSMO_ECU_CODEC_FR);
 	uint8_t frame[GSM_FR_BYTES];