This adds a fake toolchain for pointer compression, used for
correctness fuzzing. The toolchain enables us to have an extra build
with inverse pointer-compression defaults side-by-side.

The extra build is used similarly to existing x64/x86 comparisons,
except that we now compare builds with different compile-time flags.

Change-Id: I75491371262204b86eaa006ca8d04848f49121ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1829275Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64123}