Cover a static struct value by a preprocessor guard to prevent an "unused" warning.

Cython/Utility/AsyncGen.c

@@ -558,11 +558,13 @@ static PyMethodDef __Pyx_async_gen_asend_methods[] = {
 };
 
 
+#if CYTHON_USE_ASYNC_SLOTS
 static __Pyx_PyAsyncMethodsStruct __Pyx_async_gen_asend_as_async = {
     PyObject_SelfIter,                          /* am_await */
     0,                                          /* am_aiter */
     0                                           /* am_anext */
 };
+#endif
 
 
 static PyTypeObject __pyx__PyAsyncGenASendType_type = {