It's the missing piece for full SIGCHLD handling using signal-hook. We already have Origin::Chld for detecting child exit, child death, child stop, etc.

The way libc exposes siginfo_t is a bit weird, but I see that signal-hook has a bit of C code that handles the extraction, presumably so as to avoid libcs weirdness, so I think it would be reasonably straightforward.

I could make a PR for this if desired.