Add build flag to enable bitcode on ios

webrtc/build/ios/BUILD.gn

Index: webrtc/build/ios/BUILD.gn
diff --git a/webrtc/build/ios/BUILD.gn b/webrtc/build/ios/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..219617cb1706bc3afcce2620dded63ff1721186d
--- /dev/null
+++ b/webrtc/build/ios/BUILD.gn
@@ -0,0 +1,24 @@
+# Copyright (c) 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.
+
+# This file is only meant to be included on iOS.
+assert(is_ios)
+
+declare_args() {
+  # Enabling this option makes clang compile to an intermediate
+  # representation, and not to native code. This is preferred when
+  # including WebRTC in apps that will be sent to Apple's App Store
+  # and required for apps that run on watchOS or tvOS.
+  rtc_ios_enable_bitcode = false
+}
+
+config("rtc_ios_common_config") {
+  if (rtc_ios_enable_bitcode) {
+    cflags = [ "-fembed-bitcode" ]
+  }
+}