Fix some "unused" C compiler warnings.

Cython/Utility/AsyncGen.c

@@ -944,11 +944,13 @@ static PyMethodDef __Pyx_async_gen_athrow_methods[] = {
 };
 
 
+#if CYTHON_USE_ASYNC_SLOTS
 static __Pyx_PyAsyncMethodsStruct __Pyx_async_gen_athrow_as_async = {
     PyObject_SelfIter,                          /* am_await */
     0,                                          /* am_aiter */
     0                                           /* am_anext */
 };
+#endif
 
 
 static PyTypeObject __pyx__PyAsyncGenAThrowType_type = {

Cython/Utility/Coroutine.c

@@ -1465,7 +1465,7 @@ static PyObject *__Pyx_Coroutine_await(PyObject *coroutine) {
 }
 
 static PyObject *
-__Pyx_Coroutine_get_frame(__pyx_CoroutineObject *self)
+__Pyx_Coroutine_get_frame(CYTHON_UNUSED __pyx_CoroutineObject *self)
 {
     // Fake implementation that always returns None, but at least does not raise an AttributeError.
     Py_RETURN_NONE;