make CyFunction's inheritance from PyCFunction visible at the Python level to...

make CyFunction's inheritance from PyCFunction visible at the Python level to let inspect.isbuiltin(cyfunction) return True

--HG--
extra : transplant_source : %8D%99%BA%9D%13e%1E%9E%A8%88%9D%88m%F4D%DFw_%2B%F2

Cython/Utility/CythonFunction.c

@@ -644,6 +644,10 @@ static int __Pyx_CyFunction_init(void) {
 #if !CYTHON_COMPILING_IN_PYPY
     // avoid a useless level of call indirection
     __pyx_CyFunctionType_type.tp_call = PyCFunction_Call;
+#endif
+#if CYTHON_COMPILING_IN_CPYTHON
+    // make inheritance from Python's builtin function type official
+    __pyx_CyFunctionType_type.tp_base = &PyCFunction_Type;
 #endif
     __pyx_CyFunctionType = __Pyx_FetchCommonType(&__pyx_CyFunctionType_type);
     if (__pyx_CyFunctionType == NULL) {