OK, I remember again with `build_options` was also required in the modules tool classes.

In #861, the idea came forward to add an option to skip the `spider` thing that updates the (local) Lmod cache after a successful build.

That would involve something like `--skip-modules-tool-update`, and that build option needs to trickle through to the `Lmod.update()` method...

Who knows what other options need to make it down to into the modules tool classes later...