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/src/vty/cpu_sched_vty.c b/src/vty/cpu_sched_vty.c
index dbb3cd5..301e7a6 100644
--- a/src/vty/cpu_sched_vty.c
+++ b/src/vty/cpu_sched_vty.c
@@ -89,7 +89,7 @@
 };
 
 /* returns number of configured CPUs in the system, or negative otherwise */
-static int get_num_cpus() {
+static int get_num_cpus(void) {
 	static unsigned int num_cpus = 0;
 	long ln;