The util.format %f branch for boolean and unit arguments discarded the
lowered value and lowered the argument node again as a statement, so
anything lowering builds for the argument (lifted array helpers,
closures) was built twice, one copy dead. It now evaluates the value it
already lowered as a statement, and drops it when evaluating it has no
observable effect.
The same branch now also covers void calls and null | undefined unions,
which Node formats as NaN like undefined and null; they were refused.
