Updated patch. Note that I can't get it to build the same derivation
twice:
```
output ‘/gnu/store/k22jfy6asbwsxbmmajgghcnnrz6dgaqi-carla-2.0.0’ of
‘/gnu/store/nlyk7zhcnq0fl57z95qyf78gf4qsbl2r-carla-2.0.0.drv’ differs
from ‘/gnu/store/k22jfy6asbwsxbmmajgghcnnrz6dgaqi-carla-2.0.0-check’
from previous round
```