Add support for Mac OS X 64bit builds with GYP

build/common.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 261 matching lines @@
             'ldflags': [ '-m32' ],
           }],
           [ 'v8_no_strict_aliasing==1', {
             'cflags': [ '-fno-strict-aliasing' ],
           }],
         ],  # conditions
       }],
       ['OS=="solaris"', {
         'defines': [ '__C99FEATURES__=1' ],  # isinf() etc.
       }],
+      ['OS=="mac" and target_arch=="ia32"', {
+        'xcode_settings': {
+          'ARCHS': ['i386']
+        }
+      }],
+      ['OS=="mac" and target_arch=="x64"', {
+        'xcode_settings': {
+          'ARCHS': ['x86_64']
+        }
+      }],
     ],  # conditions
     'configurations': {
       'Debug': {
         'defines': [
           'DEBUG',
           'ENABLE_DISASSEMBLER',
           'V8_ENABLE_CHECKS',
           'OBJECT_PRINT',
         ],
         'msvs_settings': {
@@ skipping 102 matching lines @@
                 # some test cases can cause stack overflow.
                 # 'StackReserveSize': '297152',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }