Fix some compile warnings

src/core/macfslistener.mm

@@ -49,7 +49,7 @@ void MacFSListener::EventStreamCallback(ConstFSEventStreamRef stream, void* user
 
   MacFSListener* me = reinterpret_cast<MacFSListener*>(user_data);
   char** paths = reinterpret_cast<char**>(event_paths);
-  for (int i = 0; i < num_events; ++i) {
+  for (size_t i = 0; i < num_events; ++i) {
     QString path = QString::fromUtf8(paths[i]);
     qLog(Debug) << "Something changed at:" << path;
     while (path.endsWith('/')) {

src/device/macosdevicelister.mm

@@ -533,10 +533,10 @@ void MacOsDeviceLister::USBDeviceAddedCallback(void* refcon, io_iterator_t it) {
       device.address = [addr intValue];
 
       // First check the libmtp device list.
-      QSet<MTPDevice>::const_iterator it = sMTPDeviceList.find(device);
-      if (it != sMTPDeviceList.end()) {
+      QSet<MTPDevice>::const_iterator it2 = sMTPDeviceList.find(device);
+      if (it2 != sMTPDeviceList.end()) {
         // Fill in quirks flags from libmtp.
-        device.quirks = it->quirks;
+        device.quirks = it2->quirks;
         me->FoundMTPDevice(device, GetSerialForMTPDevice(object));
         continue;
       }

src/engine/macosdevicefinder.cpp

@@ -81,7 +81,7 @@ QList<DeviceFinder::Device> MacOsDeviceFinder::ListDevices() {
   if (!devices.get()) {
     return ret;
   }
-  const int device_count = device_size_bytes / sizeof(AudioDeviceID);
+  const UInt32 device_count = device_size_bytes / sizeof(AudioDeviceID);
 
   address.mScope = kAudioDevicePropertyScopeOutput;
   for (UInt32 i = 0; i < device_count; ++i) {