Add void to function signature

Bug: b/229823175
Change-Id: If8dd34591284c5fe9b13de7d1053db3528424515
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/259522
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Christoffer Jansson <jansson@google.com>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36587}

examples/objc/AppRTCMobile/common/ARDUtilities.m

@@ -94,7 +94,7 @@
 
 @end
 
-NSInteger ARDGetCpuUsagePercentage() {
+NSInteger ARDGetCpuUsagePercentage(void) {
   // Create an array of thread ports for the current task.
   const task_t task = mach_task_self();
   thread_act_array_t thread_array;