Ensure that the "padding" (actually needed for crashpad) is allocated
at the beginning of the new code space.

R=ahaas@chromium.org

Bug: v8:9477
Change-Id: I44b9e9feb559788e286fd5c57df90db7cf7f5340
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1803650
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63790}