Breakpad used to put a custom identifier 0x8003 into minidumps to
indicate arm64 architecture. Crashpad now uses the new standardized
value 12. This CL updates grokdump.py to understand both.

Change-Id: Ie9bf5106beba8059e89a48d42d32ac8069493925
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1648258
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62047}