os/exec: use pidfd for waiting and signaling of processes

[mitar]

Using pidfd allows us to have a handle on the process and poll the handle to non-blocking wait for the process to exit.

Fixes #34396
Fixes #60321
Fixes #60320

[gopherbot]

This PR (HEAD: 14ffe54) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/go/+/498615 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

This PR (HEAD: 86ae506) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/go/+/498615 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

This PR (HEAD: 9459756) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/go/+/498615 to see it.

Tip: You can toggle comments from me using the comments slash command (e.g. /comments off)
See the Wiki page for more info

[gopherbot]

Message from Mitar:

Patch Set 2:

(14 comments)

---

Please don’t reply on this GitHub thread. Visit golang.org/cl/498615.
After addressing review feedback, remember to publish your drafts!

[seankhliao]

stale?

[mitar]

It is not stale, but no feedback was given on the CR. :-(

So I would be really sad if this is just closed. Please review the CR instead.