Build dynamic iOS SDK.

webrtc/sdk/objc/WebRTC-Prefix.pch

 /*
  *  Copyright 2016 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.
  */
 
 #ifdef __OBJC__
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 #if !defined(__has_feature) || !__has_feature(nullability)
 #error "This file requires nullability support."
 #endif
 
+#import <Foundation/Foundation.h>
+
 // The following nonnull macros were introduced in OSX SDK 10.10.3. However,
 // the bots appear to be running something older. We define them here if they
-// aren't already defined in NSObjCRuntime.h
-#include <Foundation/NSObjCRuntime.h>
+// aren't already defined in NSObjCRuntime.h, which is included by
+// Foundation/Foundation.h.
 
 #if !defined(NS_ASSUME_NONNULL_BEGIN)
 #define NS_ASSUME_NONNULL_BEGIN
 #endif
 
 #if !defined(NS_ASSUME_NONNULL_END)
 #define NS_ASSUME_NONNULL_END
 #endif
 
 #endif  // __OBJC__