`last` indicates that it's the last element of the list but in reality
this supposed to indicate the previous entry in the list. Rename this
to something more clearer.

Change-Id: I26c9a1fca02cf6b10d0447768da694d590a43932
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2637229Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72167}