setup.py: also mock ctypes.WinDLL when building documentation.

We mock ctypes.CDLL when building documentation so that the library
does not need to be installed on the system.  But in some cases, WinDLL
is used instead.  Mock it for the same reasons.

Author: carandraug

setup.py

@@ -113,7 +113,9 @@ def run(self):
             ])
 
             with unittest.mock.patch('ctypes.CDLL', new=cdll_diversion):
-                super().run()
+                with unittest.mock.patch('ctypes.WinDLL', new=cdll_diversion,
+                                         create=True):
+                    super().run()
 
 else:
     class BuildDoc(distutils.cmd.Command):