cmd/internal/obj: stack bounds check prologue can be preemptible and resume at entry

[zhouguangyuan0718]

The stack bounds check prologue is nonpreemptible now. But actually, if we mark the unsafepoint of it as "RestartAtEntry", it can be async preempted safely. After async preempted, we just need resume it at the entry of the function.

And according to the comment in CL 208126:

TODO: the split-stack function prologue is currently not async
preemptible. We could use this mechanism, preempt it and restart
at the function entry.

It will be reasonable to do this.

[gopherbot]

Change https://go.dev/cl/525316 mentions this issue: cmd/internal/obj: mark stack bounds check prologue preemptible

[cherrymui]

This doesn't really need an issue. You can just send a CL (as you already did) and we can go from there (and have the discussion in one place). Thanks.