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: I861be39275b40c522c02f553074c5a4489e87127
diff --git a/src/mslookup_server_mdns.c b/src/mslookup_server_mdns.c
index a669526..3c7606a 100644
--- a/src/mslookup_server_mdns.c
+++ b/src/mslookup_server_mdns.c
@@ -121,7 +121,7 @@
 	talloc_free(server);
 }
 
-void mslookup_server_mdns_config_apply()
+void mslookup_server_mdns_config_apply(void)
 {
 	/* Check whether to start/stop/restart mDNS server */
 	bool should_run;