make embedding code for PEP 489 less hackish by using the official C-API functions

Cython/Utility/Embed.c

@@ -33,14 +33,17 @@ static int __Pyx_main(int argc, wchar_t **argv) {
       #if PY_MAJOR_VERSION < 3
           init%(module_name)s();
       #elif CYTHON_PEP489_MULTI_PHASE_INIT
-          {
+          m = PyInit_%(module_name)s();
+          if (!PyModule_Check(m)) {
+              PyModuleDef *mdef = (PyModuleDef *) m;
               PyObject *modname = PyUnicode_FromString("__main__");
+              m = NULL;
               if (modname) {
-                  // FIXME: not currently calling create() here because we do not have a module spec!
+                  // FIXME: not currently calling PyModule_FromDefAndSpec() here because we do not have a module spec!
                   // FIXME: not currently setting __file__, __path__, __spec__, ...
                   m = PyModule_NewObject(modname);
                   Py_DECREF(modname);
-                  if (m) __pyx_pymod_exec_%(module_name)s(m);
+                  if (m) PyModule_ExecDef(m, mdef);
               }
           }
       #else