The behavior of handlers registered with signal(3p) is not well-defined
for signals delivered more than once, as laid out in the man page.
We should replace our use of signal with sigaction, but for SIGCHLD
specifically we can also just skip the signals altogether by setting the
handler to SIG_IGN which causes child reaping to not be required.
Fixes: https://github.com/swaywm/sway/pull/8567