Fix missing import in libregrtest.
diff --git a/Lib/test/libregrtest/cmdline.py b/Lib/test/libregrtest/cmdline.py
index 21c3e66..a9cee6e 100644
--- a/Lib/test/libregrtest/cmdline.py
+++ b/Lib/test/libregrtest/cmdline.py
@@ -1,5 +1,6 @@
 import argparse
 import os
+import sys
 from test import support