Because actual condition code used by s390/ppc does not distinguish
between signed and unsigned, we need to use a generic enum class for
liftoff which needs to deal with signed/unsigned case differently.

Change-Id: Ia870dc30788037996dc1c65de0117eac7d941697
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2560603
Commit-Queue: Junliang Yan <junyan@redhat.com>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71433}