Pass -Wno-header-guard when using Clang to avoid reporting the following error in the system NSS he…

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 3063 matching lines @@
 
               # Clang spots more unused functions.
               '-Wno-unused-function',
 
               # Warns on switches on enums that cover all enum values but
               # also contain a default: branch. Chrome is full of that.
               '-Wno-covered-switch-default',
 
               # Warns when a const char[] is converted to bool.
               '-Wstring-conversion',
+
+              # Clang reports an incorrect define guard in
+              # /usr/include/nss/secmod.h

[wtc, 2013/06/19 20:01:22]

I forgot to add: please add the upstream NSS bug URL
    https://bugzilla.mozilla.org/show_bug.cgi?id=884072
to this comment, so we know when this flag can be removed.

+              '-Wno-header-guard',
+                
             ],
             'cflags!': [
               # Clang doesn't seem to know know this flag.
               '-mfpmath=sse',
             ],
           }],
           ['clang==1 and OS!="android"', {
             # Turn on C++11.
             'cflags': [
               # This warns on using ints as initializers for floats in
@@ skipping 1478 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }