Allow (and ignore) empty defines of Py_TPFLAGS_METHOD_DESCRIPTOR.

Cython/Utility/ObjectHandling.c

@@ -1485,10 +1485,10 @@ static int __Pyx_PyObject_GetMethod(PyObject *obj, PyObject *name, PyObject **me
     descr = _PyType_Lookup(tp, name);
     if (likely(descr != NULL)) {
         Py_INCREF(descr);
-        // Repeating the condition below accommodates for MSVC's inability to test macros inside of macro expansions.
-#ifdef Py_TPFLAGS_METHOD_DESCRIPTOR
+#if defined(Py_TPFLAGS_METHOD_DESCRIPTOR) && Py_TPFLAGS_METHOD_DESCRIPTOR
         if (PyType_HasFeature(Py_TYPE(descr), Py_TPFLAGS_METHOD_DESCRIPTOR))
 #elif PY_MAJOR_VERSION >= 3
+        // Repeating the condition below accommodates for MSVC's inability to test macros inside of macro expansions.
         #ifdef __Pyx_CyFunction_USED
         if (likely(PyFunction_Check(descr) || (Py_TYPE(descr) == &PyMethodDescr_Type) || __Pyx_CyFunction_Check(descr)))
         #else