Fix Cygwin compiler issue

Modules/_struct.c

@@ -1416,7 +1416,7 @@ static PyMemberDef s_memberlist[] = {
 
 static
 PyTypeObject PyStructType = {
-	PyObject_HEAD_INIT(&PyType_Type)
+	PyObject_HEAD_INIT(NULL)
 	0,
 	"Struct",
 	sizeof(PyStructObject),
@@ -1467,6 +1467,10 @@ init_struct(void)
 	if (m == NULL)
 		return;
 
+	PyStructType.ob_type = &PyType_Type;
+	if (PyType_Ready(&PyStructType) < 0)
+		return;
+
 	/* Add some symbolic constants to the module */
 	if (StructError == NULL) {
 		StructError = PyErr_NewException("struct.error", NULL, NULL);