Update from https://crrev.com/306655

net/third_party/nss/ssl/BUILD.gn

 # Copyright (c) 2013 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.
 
 config("ssl_config") {
   include_dirs = [ "." ]
 
   if (is_mac || is_win) {
     defines = [ "NSS_PLATFORM_CLIENT_AUTH" ]
   }
-
-  if (is_clang) {
-    cflags = [
-      # There is a broken header guard in /usr/include/nss/secmod.h:
-      # https://bugzilla.mozilla.org/show_bug.cgi?id=884072
-      "-Wno-header-guard",
-    ]
-  }
 }
 
 component("libssl") {
   output_name = "crssl"
 
   sources = [
     "authcert.c",
     "cmpcert.c",
     "derive.c",
     "dtlscon.c",
@@ skipping 69 matching lines @@
 
     # Must be after ssl_config since we want our SSL headers to take
     # precedence.
     public_configs += [
       "//third_party/nss:system_nss_no_ssl_config"
     ]
   } else if (is_mac) {
     libs = [ "Security.framework" ]
   }
 
+  if (is_clang) {
+    # SSL triggers some of these Clang warnings.
+    configs -= [ "//build/config/clang:extra_warnings" ]
+  }
+
   if (is_posix) {
     sources -= [
       "win32err.c",
       "win32err.h",
     ]
   }
 
   if (is_mac || is_ios) {
     defines += [
       "XP_UNIX",
       "DARWIN",
       "XP_MACOSX",
     ]
   }
 
   if (is_mac || is_ios || is_win) {
     sources -= [
       "bodge/secitem_array.c",
     ]
     public_deps = [
       "//third_party/nss:nspr",
       "//third_party/nss:nss",
     ]
   }
 
   if (is_debug) {
     defines += [ "DEBUG" ]
   }
 }