Disable Clang's warnings about undefined pointer comparisons in Debug builds

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 3213 matching lines @@
             # TODO(phajdan.jr): Should we enable this for all of POSIX?
             'defines': ['_GLIBCXX_DEBUG=1',],
           }],
           ['release_valgrind_build==0', {
             'xcode_settings': {
               'OTHER_CFLAGS': [
                 '-fstack-protector-all',  # Implies -fstack-protector
               ],
             },
           }],
+          ['clang==1', {
+            'cflags': [
+              # Allow comparing the address of references and 'this' against 0
+              # in debug builds. Technically, these can never be null in
+              # well-defined C/C++ and Clang can optimize such checks away in
+              # release builds, but they may be used in asserts in debug builds.
+              '-Wno-undefined-bool-conversion',
+              '-Wno-tautological-undefined-compare',
+            ],
+            'xcode_settings': {
+              'OTHER_CFLAGS': [
+                '-Wno-undefined-bool-conversion',
+                '-Wno-tautological-undefined-compare',
+              ],
+            },
+            'msvs_settings': {
+              'VCCLCompilerTool': {
+                'AdditionalOptions': [
+                  '-Wno-undefined-bool-conversion',
+                  '-Wno-tautological-undefined-compare',
+                ],
+              },
+            },
+          }],
         ],
       },
       'Release_Base': {
         'abstract': 1,
         'defines': [
           'NDEBUG',
         ],
         'xcode_settings': {
           'DEAD_CODE_STRIPPING': 'YES',  # -Wl,-dead_strip
           'GCC_OPTIMIZATION_LEVEL': '<(mac_release_optimization)',
@@ skipping 2439 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',
   },
 }