We can bump it up later if there is need.

Taking digit size into account for the max length in digits
makes the max length in bits consistent across architectures.

Bug: v8:6791
Change-Id: Id5205d2d308bbe6a38f8ff1ee19c082bedbeb74a
Reviewed-on: https://chromium-review.googlesource.com/717176
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48514}