So now I remember why kdesrc-build didn't recursively include
dependencies.... we took advantage of the fact that dependencies in
kdesrc-build were just for ordering (not for generating the build list)
by using 'kf5umbrella' as a fake module. This allowed workspace modules
to depend on only kf5umbrella instead of all of the frameworks
individually.

The recent changes to support recursive dependencies broke this, but I
wasn't able to reproduce until I introduce a module-set that actually
ran directly across kf5umbrella as a dependency, which is why I didn't
catch earlier.

This is only a workaround for kf5umbrella in particular, but should tide
things over until I can understand and fix it properly. Apologies for
the inconvenience.