Disable warning for signed/unsigned mismatch in MSVC

BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//testing/test.gni")
 
 config("libsrtp_config") {
   defines = [
     # Package identity
     "PACKAGE_STRING=\"libsrtp2 2.0.0-pre\"",
@@ skipping 31 matching lines @@
   # Supports clients depending on SRTP_RELATIVE_PATH.
   # TODO(mattdr): Remove SRTP_RELATIVE_PATH and this config.
   include_dirs = [
     ".",
     "config",
     "include",
     "crypto/include",
   ]
 }
 
+config("libsrtp_warnings") {
+  cflags = []
+  if (is_win) {
+    cflags += [ "/wd4018" ]  # Signed/unsigned mismatch in comparison
+  }
+}
+
 static_library("libsrtp") {
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [ ":libsrtp_warnings" ]
   public_configs = [ ":libsrtp_config" ]
   sources = [
     # includes
     "include/ekt.h",
     "include/rtp.h",
     "include/srtp.h",
 
     # headers
     "crypto/include/aes.h",
     "crypto/include/aes_gcm_ossl.h",
@@ skipping 36 matching lines @@
     "srtp/ekt.c",
     "srtp/srtp.c",
   ]
   public_deps = [
     "//third_party/boringssl:boringssl",
   ]
 }
 
 config("srtp_test_config") {
   include_dirs = [ "test" ]
+
+  configs = [ ":libsrtp_warnings" ]
+
+  cflags = []
+  if (is_win && is_clang) {

[kjellander_chromium, 2016/10/12 22:59:48]

Does this work even if it's not in a config? Because in my experience that was
not the case many times when I was battling with Win Clang errors in WebRTC.
I was just hoping you're certain or has tested this.

[mattdr-at-chromium, 2016/10/12 23:01:26]

This is in a config, now, so it should come in after the cflags in
no_chromium_code.

[kjellander_chromium, 2016/10/12 23:56:52]

Oh, I dunno why I didn't see it was in a config already, sorry ;)

+    # TODO(mattdr): Bring in https://github.com/cisco/libsrtp/pull/213
+    # and remove this.
+    cflags += [ "-Wno-format" ]
+  }
 }
 
 template("srtp_test") {
   test("srtp_test_${target_name}") {
     configs -= [ "//build/config/compiler:chromium_code" ]
     configs += [ "//build/config/compiler:no_chromium_code" ]
     configs += [ ":srtp_test_config" ]
     deps = [
       ":libsrtp",
     ]
@@ skipping 98 matching lines @@
     ":srtp_test_dtls_srtp_driver",
     ":srtp_test_kernel_driver",
     ":srtp_test_rdbx_driver",
     ":srtp_test_replay_driver",
     ":srtp_test_roc_driver",
     ":srtp_test_rtpw",
     ":srtp_test_srtp_driver",
   ]
   testonly = true
 }