Set the gyp DEPTH variable as relative path.

build/gyp_v8

 #!/usr/bin/env python
 #
 # 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
@@ skipping 127 matching lines @@
       args.extend(shlex.split(gyp_file))
     else:
       args.append(os.path.join(script_dir, 'all.gyp'))
 
   args.extend(['-I' + i for i in additional_include_files(args)])
 
   # There shouldn't be a circular dependency relationship between .gyp files
   args.append('--no-circular-check')
 
   # Set the GYP DEPTH variable to the root of the V8 project.
-  args.append('--depth=' + v8_root)
+  args.append('--depth=' + os.path.relpath(v8_root))
 
   # If V8_GYP_SYNTAX_CHECK is set to 1, it will invoke gyp with --check
   # to enfore syntax checking.
   syntax_check = os.environ.get('V8_GYP_SYNTAX_CHECK')
   if syntax_check and int(syntax_check):
     args.append('--check')
 
   print 'Updating projects from gyp files...'
   sys.stdout.flush()
 
   # Generate for the architectures supported on the given platform.
   gyp_args = list(args)
   if platform.system() == 'Linux':
     # --generator-output defines where the Makefile goes.
     gyp_args.append('--generator-output=out')
     # -Goutput_dir defines where the build output goes, relative to the
     # Makefile. Set it to . so that the build output doesn't end up in out/out.
     gyp_args.append('-Goutput_dir=.')
   run_gyp(gyp_args)