remove module-wide warning suppression.

The warnings in question are benign and should be supressed locally so
we can keep the analysis for the rest of the files.

BUG=webrtc:5748

Review-Url: https://codereview.webrtc.org/2790883002
Cr-Commit-Position: refs/heads/master@{#17485}

webrtc/modules/audio_device/BUILD.gn

@@ -19,14 +19,6 @@ config("audio_device_config") {
     "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.
-    # TODO(tkchin): Remove after fixing
-    # https://bugs.chromium.org/p/webrtc/issues/detail?id=5748
-    cflags = [ "-Wno-thread-safety-analysis" ]
-  }
 }
 
 config("audio_device_warnings_config") {

webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm

@@ -193,6 +193,9 @@ NSInteger const kRTCAudioSessionErrorConfiguration = -2;
   }
 }
 
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wthread-safety-analysis"
+
 - (void)lockForConfiguration {
   _crit.Enter();
   rtc::AtomicOps::Increment(&_lockRecursionCount);
@@ -210,6 +213,8 @@ NSInteger const kRTCAudioSessionErrorConfiguration = -2;
   }
 }
 
+#pragma clang diagnostic pop
+
 #pragma mark - AVAudioSession proxy methods
 
 - (NSString *)category {