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.c b/src/mslookup_server.c
index 885adf8..3771369 100644
--- a/src/mslookup_server.c
+++ b/src/mslookup_server.c
@@ -49,7 +49,7 @@
 	result->age = age;
 }
 
-const struct mslookup_service_host *mslookup_server_get_local_gsup_addr()
+const struct mslookup_service_host *mslookup_server_get_local_gsup_addr(void)
 {
 	static struct mslookup_service_host gsup_bind = {};
 	struct mslookup_service_host *host;