For robustness, also test the disposition in our own process even if other tests in `tests/ui/attributes/unix_sigpipe` already covers it.
SIGPIPE
In `auxiliary/sigpipe-utils.rs`, all we want to know is the current `SIGPIPE` disposition. We should not change it. So use `libc::sigaction` instead of `libc::signal`. That way we can also remove the code that restores it.