Fix PyVelox build by resetting ROOT_DIR (facebookincubator#9331)

Summary:
Fixes : facebookincubator#9330

PyVelox builds started failing because of change in ROOT_DIR.

Pull Request resolved: facebookincubator#9331

Reviewed By: xiaoxmeng

Differential Revision: D55618314

Pulled By: kgpai

fbshipit-source-id: a9a9cb23b848b2766820ef872f0eda862cbcd840

setup.py

@@ -159,7 +159,7 @@ def build_extension(self, ext):
             os.makedirs(self.build_temp)
 
         subprocess.check_call(
-            ["cmake", str(os.path.join(ROOT_DIR, "pyvelox"))] + cmake_args,
+            ["cmake", str(ROOT_DIR)] + cmake_args,
             cwd=self.build_temp,
         )
         subprocess.check_call(