tldr: This adds an on-demand comparison with x64 when a difference to
a non-x64 build is detected.

Normally foozzie compares the baseline build (just ignition), with
two secondary builds. One, the default, always uses the shipping
configuration, the second passes additional flags. Both can use a
different architecture than the baseline build as well.

Differences between ignition and turbofan are then often detected
independent of the architectures used, but reported several times
(for each compared architecture).

This makes the reporting more specific, by running another build on
demand that uses the baseline architecture, but otherwise the same
configuration that showed a difference. If it shows the difference as
well, the baseline architecture is used for the report.

As a result only pure architecture differences will be reported with
an architecture other than x64.

This also adds some minor refactorings to reduce the code complexity
when looping over comparisons.

For testing this, the fake-d8s are extended with different behavior
for different flags passed. We add two test cases for testing:
x64 vs. ia32 with difference in x64 and ia32
x64 vs. ia32 with difference only in ia32

Bug: chromium:1196633
No-Try: true
Test: tools/clusterfuzz/v8_foozzie_test.py
Change-Id: Ic470ae8f0b37fb1628b32e4fafc0c39377e16f8c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2897099Reviewed-by: Liviu Rau <liviurau@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74612}