Provide a V8_ASSUME implementation for GCC which has the same effect as
using __builtin_assume on clang.

R=cbruni@chromium.org

Change-Id: Ia6ab56995d9ecac1015eab8bacc7e3115da7004f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779691Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81901}