Fix Mac build after r24676.

build/standalone.gypi

 # Copyright 2012 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 118 matching lines @@
     'arm_thumb': 'default',
   },
   'target_defaults': {
     'variables': {
       'v8_code%': '<(v8_code)',
     },
     'default_configuration': 'Debug',
     'configurations': {
       'DebugBaseCommon': {
         'cflags': [ '-g', '-O0' ],
-        'defines': [
-          '_GLIBCXX_DEBUG'
+        'conditions': [
+          ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" or \
+            OS=="qnx"', {
+            'defines': [
+              '_GLIBCXX_DEBUG'
+            ],
+          }],
         ],
       },
       'Optdebug': {
         'inherit_from': [ 'DebugBaseCommon', 'DebugBase2' ],
       },
       'Debug': {
         # Xcode insists on this empty entry.
       },
       'Release': {
         # Xcode insists on this empty entry.
@@ skipping 261 matching lines @@
         ],
         'target_conditions': [
           ['_type!="static_library"', {
             'xcode_settings': {'OTHER_LDFLAGS': ['-Wl,-search_paths_first']},
           }],
         ],  # target_conditions
       },  # target_defaults
     }],  # OS=="mac"
   ],
 }