The liveness verifier will check that the live ranges are consistent
with the function. It runs as part of the register allocation pipeline
when enable_verifier is set.
The initial implementation checks the live ranges, but not the
ISA-specific constraints and affinities.
The test drivers can stop calling comp_ctx.verify because legalize() and
regalloc() do it themselves now.
This also makes it possible for those two passes to return other
CtonError codes in the future, not just verifier errors.
Run the verify_contexti() function after invoking the legalize() and
regalloc() context functions. This will help catch bad code produced by
these passes.