cmd/vet/all: work around vet printf checker deficiencies
cmd/vet has a known deficiency in its handling of fmt.Formatters.
This causes a spurious printf error only for non-host platforms.
Since cmd/vet/all may get run on any given platform,
whitelists cannot help here.
Work around the issue by skipping printf tests entirely
for non-host platforms.
Work around the one known acceptable false positive from vet
by whitelisting the file that contains it.