[gn] Move build to gypfiles

gypfiles/detect_v8_host_arch.py

 #!/usr/bin/env python
 # Copyright 2014 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
@@ skipping 57 matching lines @@
   # kernel with 32-bit userland, e.g. to give linker slightly more memory.
   # Distinguish between different userland bitness by querying
   # the python binary.
   if host_arch == 'x64' and platform.architecture()[0] == '32bit':
     host_arch = 'ia32'
 
   return host_arch
 
 if __name__ == '__main__':
   sys.exit(main())