Fixing -Wstrict-prototypes warnings.

Bug: webrtc:8984
Change-Id: I9a7ffb0038f341bfec055f021fc203c7d45d72fa
Reviewed-on: https://webrtc-review.googlesource.com/60903
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22501}
diff --git a/examples/objc/AppRTCMobile/common/ARDUtilities.h b/examples/objc/AppRTCMobile/common/ARDUtilities.h
index 8a5c126..5795ff1 100644
--- a/examples/objc/AppRTCMobile/common/ARDUtilities.h
+++ b/examples/objc/AppRTCMobile/common/ARDUtilities.h
@@ -34,5 +34,5 @@
 
 @end
 
-NSInteger ARDGetCpuUsagePercentage();
+NSInteger ARDGetCpuUsagePercentage(void);