GN: Fix iOS build.

webrtc/modules/video_render/BUILD.gn

 # Copyright (c) 2014 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.
 
 import("../../build/webrtc.gni")
 
@@ skipping 143 matching lines @@
         "ios/video_render_ios_gles20.h",
         "ios/video_render_ios_gles20.mm",
         "ios/video_render_ios_impl.h",
         "ios/video_render_ios_impl.mm",
         "ios/video_render_ios_view.h",
         "ios/video_render_ios_view.mm",
       ]
 
       deps += [ "../..:webrtc_common" ]
 
-      cflags += [ "-fobjc-arc" ]  # CLANG_ENABLE_OBJC_ARC = YES.
+      cflags = [ "-fobjc-arc" ]  # CLANG_ENABLE_OBJC_ARC = YES.
     }
 
     all_dependent_configs = [ ":video_render_internal_impl_config" ]
 
     configs += [ "../..:common_config" ]
     public_configs = [ "../..:common_inherited_config" ]
 
     if (is_clang) {
       # Suppress warnings from Chrome's Clang plugins.
       # See http://code.google.com/p/webrtc/issues/detail?id=163 for details.
       configs -= [ "//build/config/clang:find_bad_constructs" ]
     }
   }
 }