init: enable 'user root' check at build time

For visibility.

We could make this only for new API levels, but it isn't
currently exposed at build time, and visibility is good
on upgrades.

Bug: 340953047
Test: build, on device passing and failing requirements
Change-Id: I3a0ea47560c65114bc1b8685954d1fb7687cb8df
3 files changed