Set the gyp DEPTH variable as relative path.

After r18439, it's an absolute variable which confuses gy

LOG=n
R=ulan@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/119293004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@18440 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/gyp_v8

@@ -145,7 +145,7 @@ if __name__ == '__main__':
   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.