>=>You don't need to make libkern.
>
>   This may be so, but "make build" currently attempts to do so (by
>making in sys, which makes in lib, which makes in libkern), and
>so fails. In fact, a plain "make" would basically do the same thing.
>This really should be fixed.

Yep. So which targets should not proceed to sys or what is the stage
where the descend should be cut for which targets? I suppose there
should be some .if target() wrappers around some SUBDIR+= lines.