sysklogd: fix compile error (#18133)

sysklogd was failing to build because it didn't know the size of the
`union wait` type.

Running `git bisect` showed 9744c776,
which bumped glibc from 2.23 to 2.24, as the likely suspect.  This is
corroborated by evidence such as this email:
https://lists.debian.org/debian-glibc/2016/08/msg00069.html

Linux from scratch recommends changing `union wait` to `int`:
http://www.linuxfromscratch.org/lfs/view/development/chapter06/sysklogd.html

Therefore, that's what this commit does.