GeezerVison

#49703 cherry-picked a commit from upstream V8 which references some maglev-related flags that are not present in the version of V8 in Node.js 20.

V8 CI on x64 is currently broken, e.g. https://ci.nodejs.org/job/node-test-commit-v8-linux/5892/nodes=benchmark-ubuntu2204-intel-64,v8test=v8test/console

16:38:36 ../../src/flags/flags.cc:590:33: error: no member named 'maglev_deopt_data_on_background' in 'v8::internal::FlagValues'
16:38:36         flag.PointsTo(&v8_flags.maglev_deopt_data_on_background) ||
16:38:36                        ~~~~~~~~ ^
16:38:36 ../../src/flags/flags.cc:591:33: error: no member named 'maglev_build_code_on_background' in 'v8::internal::FlagValues'
16:38:36         flag.PointsTo(&v8_flags.maglev_build_code_on_background) ||
16:38:36                        ~~~~~~~~ ^
16:38:36 2 errors generated.

This comes from #49703 which went out in Node.js 20.8.0 and was presumably missed because the x64 V8 CI has been unreliable due to networking issues on the machine. The V8 CI has been moved onto new x64 machines, which have revealed this compilation failure. (Other release lines successfully compile but are failing perf-related tests.)

Other platforms tested in the V8 CI, Linux on ppc64le and s390x, do not enable maglev so didn't surface this.

This is a fairly naive attempt to fix the compilation failure -- I don't know if there are alternate flags for the version of V8 in Node.js 20 that should be implied by --predictable. cc @joyeecheung