Introduce a notion of "v8_code" in gyp config files.

tools/gyp/v8.gyp

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 {
+  'variables': {
+    'v8_code': 1,
+  },
   'includes': ['../../build/common.gypi'],
   'targets': [
     {
       'target_name': 'v8',
       'dependencies_traverse': 1,
       'conditions': [
         ['want_separate_host_toolset==1', {
           'toolsets': ['host', 'target'],
         }, {
           'toolsets': ['target'],
@@ skipping 888 matching lines @@
         }],
         ['v8_compress_startup_data=="bz2"', {
           'libraries': [
             '-lbz2',
           ]
         }],
       ],
     },
   ],
 }