[clang] Set correct clang warning flags.

build/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 147 matching lines @@
       'variables': {
         'target_cxx_is_biarch%': 1,
        },
      }, {
       'variables': {
         'target_cxx_is_biarch%': 0,
       },
     }],
   ],
   'target_defaults': {
+    'variables': {
+      'clang_warning_flags': [
+        '-Wheader-hygiene',
+
+        # Warns when a const char[] is converted to bool.
+        '-Wstring-conversion',
+      ],
+    },
+    'includes': [ 'set_clang_warning_flags.gypi', ],
     'conditions': [
       ['v8_target_arch=="arm"', {
         'defines': [
           'V8_TARGET_ARCH_ARM',
         ],
         'conditions': [
           [ 'arm_version==7 or arm_version=="default"', {
             'defines': [
               'CAN_USE_ARMV7_INSTRUCTIONS',
             ],
@@ skipping 1085 matching lines @@
           ['v8_enable_slow_dchecks==1', {
             'defines': [
               'ENABLE_SLOW_DCHECKS',
             ],
           }],
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }