GN: Fix some build errors for iOS.

webrtc/modules/audio_device/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")
 
 config("audio_device_config") {
   include_dirs = [
     "../include",
     "include",
     "dummy",  # Contains dummy audio device implementations.
   ]
+  if (is_ios) {
+    # GN orders flags on a target before flags from configs. In order to be able
+    # suppress the -Wthread-safety-analysis warning, it has come from a config
+    # and can't be on the target directly.
+    cflags = [ "-Wno-thread-safety-analysis" ]

[kjellander_webrtc, 2016/04/06 17:12:35]

Zeke: do you think a bug should be filed for this, in case the error is
something you want to take a look at?
It looked like this:

../../webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm:156:3: error:
cannot resolve lock expression [-Werror,-Wthread-safety-analysis]
  _crit.Enter();
  ^~~~~
../../webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm:163:7: error:
cannot resolve lock expression [-Werror,-Wthread-safety-analysis]
  if (_crit.TryEnter()) {
      ^~~~~
../../webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm:167:5: error:
cannot resolve lock expression [-Werror,-Wthread-safety-analysis]
    _crit.Leave();
    ^~~~~
../../webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm:168:5: error:
cannot resolve lock expression [-Werror,-Wthread-safety-analysis]
    _crit.Leave();
    ^~~~~
4 errors generated.

[tkchin_webrtc, 2016/04/06 19:23:17]

File a bug. Should be suppressed manually in the implementation file. These
warnings are benign.

+  }
 }
 
 source_set("audio_device") {
   deps = [
     "../..:webrtc_common",
     "../../base:rtc_base_approved",
     "../../common_audio",
     "../../system_wrappers",
     "../utility",
   ]
@@ skipping 114 matching lines @@
         "ios/objc/RTCAudioSession.h",
         "ios/objc/RTCAudioSession.mm",
         "ios/objc/RTCAudioSessionConfiguration.h",
         "ios/objc/RTCAudioSessionConfiguration.m",
         "ios/objc/RTCAudioSessionDelegateAdapter.h",
         "ios/objc/RTCAudioSessionDelegateAdapter.mm",
         "ios/voice_processing_audio_unit.h",
         "ios/voice_processing_audio_unit.mm",
       ]
       cflags += [ "-fobjc-arc" ]  # CLANG_ENABLE_OBJC_ARC = YES.
+
       libs = [
         "AudioToolbox.framework",
         "AVFoundation.framework",
         "Foundation.framework",
         "UIKit.framework",
       ]
     }
     if (is_win) {
       sources += [
         "win/audio_device_core_win.cc",
@@ skipping 28 matching lines @@
     "../..:common_inherited_config",
     ":audio_device_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" ]
   }
 }