_Gdeadextra is almost the same as _Gdead but for goroutines attached to
extra Ms. The primary difference is that it can be transitioned into a
_Gscan status, unlike _Gdead. (Why not just use _Gdead? For safety,
mostly. There's exactly one case where we're going to want to transition
_Gdead to _Gscan|_Gdead, and it's for extra Ms. It's also a bit weird to
call this state dead when it can still have a syscalling P attached to
it.)
This status is used in a follow-up change that changes entersyscall and
exitsyscall.
Change-Id: I169a4c8617aa3dc329574b829203f56c86b58169
Reviewed-on: https://go-review.googlesource.com/c/go/+/646197 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>