Flags need to be set before initializing V8.

R=cbruni@chromium.org

Bug: v8:12887
Change-Id: Idb815a6a85ccb86c79d826da487a7bbc6fab7d1a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3707096
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81178}