Unfortunately heap setup happens before setting up flags in practice.
This means that flags such as `--single-threaded-gc` were not respected
properly for Oilpan. Delay the setup until the GC is actually triggered.

Bug: chromium:1326723
Change-Id: Icabe7ecf27e879bd44bba5e09ca176beb012c58a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3657430Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80667}