Explicitly specify the enum base type for Flags enums generated
from Torque bitfield structs. Before, this was implicitly a signed
integer type. This caused a recent gcc compile issue with signed
and unsigned comparisons triggered by
https://chromium-review.googlesource.com/c/v8/v8/+/3251177

Bug: v8:7793
Change-Id: Iceb3c8632cfc95766b5e6ce7fae47cf5d002b9f7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3253358
Auto-Submit: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77658}