Fix "unused function" warning by marking as unused

- I'm assuming that the reason this is still around is that
  it's useful to have around when debugging. If it's actually
  not used then it's probably best to just delete it.

Core/Contents/Source/PolyCocoaCore.mm

@@ -587,6 +587,8 @@ static void hatValueToXY(CFIndex value, CFIndex range, int * outX, int * outY) {
 }
 
 
+// Marked as unused to avoid a warning, assuming that this is useful for debugging.
+__attribute__((unused))
 static int IOHIDDeviceGetIntProperty(IOHIDDeviceRef deviceRef, CFStringRef key) {
 	CFTypeRef typeRef;
 	int value;