Compile rtc_base_objc and rtc_api_objc for Mac

webrtc/api/objc/WebRTC-Prefix.pch

Index: webrtc/api/objc/WebRTC-Prefix.pch
diff --git a/webrtc/api/objc/WebRTC-Prefix.pch b/webrtc/api/objc/WebRTC-Prefix.pch
deleted file mode 100644
index 990b1602da936a98a04b315411b2487aaaf904e5..0000000000000000000000000000000000000000
--- a/webrtc/api/objc/WebRTC-Prefix.pch
+++ /dev/null
@@ -1,13 +0,0 @@
-/*
- *  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.
- */
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif