build: make python executable configurable

tools/gyp/v8.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 784 matching lines @@
             {
               'action_name': 'js2c',
               'inputs': [
                 '../../tools/js2c.py',
                 '<@(library_files)',
               ],
               'outputs': [
                 '<(SHARED_INTERMEDIATE_DIR)/libraries.cc',
               ],
               'action': [
-                'python',
+                '<(python)',
                 '../../tools/js2c.py',
                 '<@(_outputs)',
                 'CORE',
                 '<(v8_compress_startup_data)',
                 '<@(library_files)'
               ],
             },
             {
               'action_name': 'js2c_experimental',
               'inputs': [
                 '../../tools/js2c.py',
                 '<@(experimental_library_files)',
               ],
               'outputs': [
                 '<(SHARED_INTERMEDIATE_DIR)/experimental-libraries.cc',
               ],
               'action': [
-                'python',
+                '<(python)',
                 '../../tools/js2c.py',
                 '<@(_outputs)',
                 'EXPERIMENTAL',
                 '<(v8_compress_startup_data)',
                 '<@(experimental_library_files)'
               ],
             },
           ],
         },
         {
           'target_name': 'postmortem-metadata',
           'type': 'none',
           'variables': {
             'heapobject_files': [
                 '../../src/objects.h',
                 '../../src/objects-inl.h',
             ],
           },
           'actions': [
               {
                 'action_name': 'gen-postmortem-metadata',
                 'inputs': [
                   '../../tools/gen-postmortem-metadata.py',
                   '<@(heapobject_files)',
                 ],
                 'outputs': [
                   '<(SHARED_INTERMEDIATE_DIR)/debug-support.cc',
                 ],
                 'action': [
-                  'python',
+                  '<(python)',
                   '../../tools/gen-postmortem-metadata.py',
                   '<@(_outputs)',
                   '<@(heapobject_files)'
                 ]
               }
            ]
         },
         {
           'target_name': 'mksnapshot',
           'type': 'executable',
@@ skipping 143 matching lines @@
             }],
           ],
           'dependencies': [
             'v8'
           ],
         },
       ],
     }],
   ],
 }