message: fallback functions ENOKI_AUTODIFF=0 case
diff: @@ -132,6 +132,9 @@ PYBIND11_MODULE(enoki_ext, m_) {
  m.def("ad_whos", []() { py::print(ek::ad_whos()); });
  m.def("ad_enabled", &ek::ad_enabled);
  m.def("ad_set_enabled", &ek::ad_set_enabled);
  +#else
  + m.def("ad_enabled", []() { return false; });
  + m.def("ad_set_enabled", [](bool) { });
  #endif
  struct Scope {
  