build: [BREAKING CHANGE] Add dependency expression

The main immediate effect of this is to remove the mobile-specific items
from the current built targets, all of which are intended to be desktop-
only. Later we can add mobile-specific build targets, but that is not to
be done trivially.

Change-Id: I9e888c87bd1fa6629c7481f1f3339ad25df61cbb
Merge "build: [BREAKING CHANGE] Add dependency expression"