The serializer currently cannot handle a heap state containing
arbitrary compiled Code objects. As a quick fix for the
--stress-snapshot d8 flag, we clear compiled data from the isolate
prior to the serialize-deserialize-verify pass.

With this change, mjsunit tests pass on x64.

The %SerializeDeserializeNow() runtime function would require more
work, since it is not possible to mutate the heap to this extent while
still preserving a runnable host context and isolate. We will need
another solution there.

Drive-by: Skip the stress_snapshot variant except for the mjsunit
suite.

Tbr: machenbach@chromium.org
Bug: v8:10493,v8:10416
Change-Id: Ie110da8b51613fcd69c7f391d3cf8589d6b04dd8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2182429Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67585}