Enable the -Wundef warning for clang

webrtc/sdk/objc/Framework/Classes/avfoundationvideocapturer.mm

 /*
  *  Copyright 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 286 matching lines @@
 - (void)captureOutput:(AVCaptureOutput *)captureOutput
     didDropSampleBuffer:(CMSampleBufferRef)sampleBuffer
          fromConnection:(AVCaptureConnection *)connection {
   RTCLogError(@"Dropped sample buffer.");
 }
 
 #pragma mark - AVCaptureSession notifications
 
 - (void)handleCaptureSessionInterruption:(NSNotification *)notification {
   NSString *reasonString = nil;
-#if defined(__IPHONE_9_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_9_0
+#if defined(__IPHONE_9_0) && defined(__IPHONE_OS_VERSION_MAX_ALLOWED) \
+    && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_9_0
   NSNumber *reason =
       notification.userInfo[AVCaptureSessionInterruptionReasonKey];
   if (reason) {
     switch (reason.intValue) {
       case AVCaptureSessionInterruptionReasonVideoDeviceNotAvailableInBackground:
         reasonString = @"VideoDeviceNotAvailableInBackground";
         break;
       case AVCaptureSessionInterruptionReasonAudioDeviceInUseByAnotherClient:
         reasonString = @"AudioDeviceInUseByAnotherClient";
         break;
@@ skipping 86 matching lines @@
     }
   }];
 }
 
 #endif  // TARGET_OS_IPHONE
 
 #pragma mark - Private
 
 - (BOOL)setupCaptureSession {
   AVCaptureSession *captureSession = [[AVCaptureSession alloc] init];
-#if defined(__IPHONE_7_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_7_0
+#if defined(__IPHONE_7_0) && defined(__IPHONE_OS_VERSION_MAX_ALLOWED) \
+    && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_7_0
   NSString *version = [[UIDevice currentDevice] systemVersion];
   if ([version integerValue] >= 7) {
     captureSession.usesApplicationAudioSession = NO;
   }
 #endif
 
   // Add the output.
   AVCaptureVideoDataOutput *videoDataOutput = [self videoDataOutput];
   if (![captureSession canAddOutput:videoDataOutput]) {
     RTCLogError(@"Video data output unsupported.");
@@ skipping 331 matching lines @@
       buffer = rotated_buffer;
     }
   }
 
   OnFrame(cricket::WebRtcVideoFrame(buffer, rotation,
                                     translated_camera_time_us, 0),
           captured_width, captured_height);
 }
 
 }  // namespace webrtc