Sparkplug is a new baseline, non-optimising second-tier compiler,
designed to fit in the compiler trade-off space between Ignition and
TurboProp/TurboFan.

Design doc:
https://docs.google.com/document/d/13c-xXmFOMcpUQNqo66XWQt3u46TsBjXrHrh4c045l-A/edit?usp=sharing

Bug: v8:11420
Change-Id: Ideb7270db3d6548eedd8337a3f596eb6f8fea6b1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2667514
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72686}