GN: Fix windows clang errors. Attempt 2.

webrtc/api/BUILD.gn

 # Copyright (c) 2015 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")
 import("//testing/test.gni")
@@ skipping 283 matching lines @@
 }
 
 if (rtc_include_tests) {
   config("peerconnection_unittests_config") {
     # The warnings below are enabled by default. Since GN orders compiler flags
     # for a target before flags from configs, the only way to disable such
     # warnings is by having them in a separate config, loaded from the target.
     # TODO(kjellander): Make the code compile without disabling these flags.
     # See https://bugs.webrtc.org/3307.
     if (is_clang && is_win) {
-      cflags = [ "-Wno-unused-function" ]
+      cflags = [
+        # See https://bugs.chromium.org/p/webrtc/issues/detail?id=6267
+        # for -Wno-sign-compare
+        "-Wno-sign-compare",
+        "-Wno-unused-function",
+      ]
     }
 
     if (!is_win) {
       cflags = [ "-Wno-sign-compare" ]
       cflags_cc = [ "-Wno-overloaded-virtual" ]
     }
   }
 
   test("peerconnection_unittests") {
     testonly = true
@@ skipping 124 matching lines @@
 
       shared_libraries = [ ":libjingle_peerconnection_so" ]
     }
 
     android_resources("libjingle_peerconnection_android_unittest_resources") {
       resource_dirs = [ "androidtests/res" ]
       custom_package = "org.webrtc"
     }
   }
 }