See comment on the macro definition. In short, pybind11 3.x added `py::native_enum`, and also had to add overhead for that new way to bind enums on the critical path for calling functions that take regular old `py::enum_`s as arguments (for example, `__eq__`). Differential Revision: [D82873169](https://our.internmc.facebook.com/intern/diff/D82873169/) Pull Request resolved: https://github.com/pytorch/pytorch/pull/163527 Approved by: https://github.com/ezyang
