Leaptiering is the new tiering

[Olivier Flückiger]

Hi all,

leaptiering is what we call a new infrastructure for tiering up functions through our different optimizing compilation tiers. It was introduced to support the sandbox [1], but to avoid having to maintain two approaches in parallel I have since ported it to all x64(-64) and arm(64) builds. I intend to enable it by default for all builds in the next 13.4 and if possible remove non-leaptiering code in 13.5.

Hence, if you help maintain a V8 port please make sure it builds and works with the gn arg `v8_enable_leaptiering = true`.

If there are any concerns or issues, reach out to me.

Cheers,

*oli

[1] https://docs.google.com/document/d/1WkyEynMluvIr0LBmrapyF7MiE8wIHFHnlP5B6FFhQuA/edit?usp=sharing