When the garbage collector needs to get a struct's type information,
it must be prepared to deal with forwarding pointers, as those will
only get cleaned up at the end of the GC cycle.

Bug: v8:7748
Change-Id: Ifdfdffcef27d1dbe07c86a3abd17711f46c1b900
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2187732
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67648}