Add build support for _elementtree on Windows.
diff --git a/Tools/msi/msi.py b/Tools/msi/msi.py
index 4998565..6dc8663 100644
--- a/Tools/msi/msi.py
+++ b/Tools/msi/msi.py
@@ -104,6 +104,7 @@
     'unicodedata.pyd',
     'winsound.pyd',
     'zlib.pyd',
+    '_elementtree.pyd',
     '_bsddb.pyd',
     '_socket.pyd',
     '_ssl.pyd',