Fix build directory cleaner, to not follow links on Windows.

tools/clean_output_directory.py

Index: tools/clean_output_directory.py
diff --git a/tools/clean_output_directory.py b/tools/clean_output_directory.py
index f94259bb610e0dab8ce21b89494745ac3f2f6cf0..e41671c4d336c24f933407f7bb060983ac22a22a 100755
--- a/tools/clean_output_directory.py
+++ b/tools/clean_output_directory.py
@@ -12,7 +12,13 @@ import utils
 def Main():
   build_root = utils.GetBuildRoot(utils.GuessOS())
   print 'Deleting %s' % build_root
-  shutil.rmtree(build_root, ignore_errors=True)
+  if sys.platform != 'win32':
+    shutil.rmtree(build_root, ignore_errors=True)
+  else:
+    # Intentionally ignore return value since a directory might be in use.
+    subprocess.call(['rmdir', '/Q', '/S', build_root],
+                    env=os.environ.copy(),
+                    shell=True)
   return 0
 
 if __name__ == '__main__':