The model where nimbus-build-system.paths were generated as a dependency
from `update-common` proved to create various issues in practice:
* It was not working properly during the repository bootstrapping
because the paths file generation script is assuming that all
submodules are already checked out
* It was not always triggered from builds of the top-level targets
due to missing or already satisfied dependencies on `update-common`.
A more proper solution would structure the dependencies like this:
top-level-project -> nimbus-build-system.paths -> vendor-modules
... but this requires a larger refactoring of the Makefiles, so I'm
merging this interim solution as a way to improve the status quo.
Zahary Karadjov