Remove the Py_TPFLAGS_HAVE_GC from the _ctypes.COMError type.

Fixes issue #4433; reviewed by Benjamin Peterson.

Misc/NEWS

@@ -24,6 +24,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #4433: Fixed an access violation when garbage collecting
+  _ctypes.COMError instances.
+
 - Issue #4429: Fixed UnicodeDecodeError in ctypes.
 
 - Issue #4373: Corrected a potential reference leak in the pickle module and

Modules/_ctypes/_ctypes.c

@@ -5097,8 +5097,7 @@ static PyTypeObject PyComError_Type = {
     0,                          /* tp_getattro */
     0,                          /* tp_setattro */
     0,                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-        | Py_TPFLAGS_HAVE_GC,   /* tp_flags */
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,   /* tp_flags */
     PyDoc_STR(comerror_doc),    /* tp_doc */
     0,                          /* tp_traverse */
     0,                          /* tp_clear */