That's the common way to do this and has the advantage that it works
when the zephyr repo is an a different location and was not registered
in the users cmake registry - which is a very common usecase supported
by zephyr. You end up with that by `west init`-ing the git url of either
the zmk repo directly or another manifest repo which imports the zmk
repo. This is more convenient than the whole manual `west init -l`
stuff.
This works because west automatically exports the `ZEPHYR_BASE`
environment variable to all extensions - including `west build`.
For that exact reason it should not break anyones scripts unless they're
using cmake directly and didn't set the $ZEPHYR_BASE environment
variable.
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