Providing physrw without providing kcall is not possible

[opa334]

Due to physrw being part of the kcall initializer, you can't provide physrw but not kcall, as the initializer checks only kcall and will discard the physrw functions even if you set them in your plugin.

[Siguza]

Okay wow, the entire plugin interface is broken.
I guess we need an RFC on whether we want to mix plugins (which seems to currently be done) or whether only one plugin should be chosen. But either of those will require some sort of grading algorithm for plugins...

As a workaround for now, it should be legal for you to export a kcall function that just returns ENOTSUP.