Treat lint warnings as errors

Warnings get lost in the build spam and never get fixed. Right now is
the best time to do this, because we only track the warnings/errors
since the last released API. The API has just been frozen, so the number
of warnings is at an all-time low.

Whitelist the car lib and test stubs for now, which produce a lot of
warnings.

Bug: 154317059
Test: presubmit
Change-Id: I9aa7cb1b947c6c664f15e2bd5835d76eaac1237a