Revert of Remove wasm compile time option and enable wasm behind a runtime flag.

src/d8.gyp

 # 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 83 matching lines @@
           'dependencies': [
             '<(icu_gyp_path):icui18n',
             '<(icu_gyp_path):icuuc',
           ],
         }],
         ['OS=="win" and v8_enable_i18n_support==1', {
           'dependencies': [
             '<(icu_gyp_path):icudata',
           ],
         }],
+        ['v8_wasm!=0', {
+          'include_dirs': ['../third_party/wasm'],
+        }],
       ],
     },
     {
       'target_name': 'd8_js2c',
       'type': 'none',
       'variables': {
         'js_files': [
           'd8.js',
           'js/macros.py',
         ],
@@ skipping 39 matching lines @@
             '../build/isolate.gypi',
           ],
           'sources': [
             'd8.isolate',
           ],
         },
       ],
     }],
   ],
 }