Make fast tls the default

src/d8.gyp

 # Copyright 2010 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 21 matching lines @@
       'type': 'executable',
       'dependencies': [
         'd8_js2c#host',
         '../tools/gyp/v8.gyp:v8',
       ],
       'include_dirs+': [
         '../src',
       ],
       'defines': [
         'ENABLE_DEBUGGER_SUPPORT',
-        'V8_FAST_TLS',
       ],
       'sources': [
         'd8.cc',
         'd8-debug.cc',
         '<(SHARED_INTERMEDIATE_DIR)/d8-js.cc',
       ],
       'conditions': [
         [ 'OS=="linux" or OS=="mac" or OS=="freebsd" or OS=="openbsd" or OS=="solaris"', {
           'sources': [ 'd8-posix.cc', ]
         }],
@@ skipping 27 matching lines @@
             '../tools/js2c.py',
             '<@(_outputs)',
             'D8',
             '<@(js_files)'
           ],
         },
       ],
     }
   ],
 }