Avoid the deprecated FLAG_* syntax, access flag values via the
{v8_flags} struct instead.

R=saelo@chromium.org

Bug: v8:12887
Change-Id: I7e41e1952958936c32fec501b8348fac0538cd71
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3899269Reviewed-by: Samuel Groß <saelo@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83265}