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 9744c7768d,
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.

pkgs/os-specific/linux/sysklogd/default.nix

@@ -8,7 +8,7 @@ stdenv.mkDerivation {
     sha256 = "00f2wy6f0qng7qzga4iicyzl9j8b7mp6mrpfky5jxj93ms2w2rji";
   };
 
-  patches = [ ./systemd.patch ];
+  patches = [ ./systemd.patch ./union-wait.patch ];
 
   NIX_CFLAGS_COMPILE = "-DSYSV";
 

pkgs/os-specific/linux/sysklogd/union-wait.patch

@@ -0,0 +1,11 @@
+--- sysklogd-1.5-old/syslogd.c	2016-08-30 22:50:59.812926945 +0100
++++ sysklogd-1.5/syslogd.c	2016-08-30 22:51:12.008842890 +0100
+@@ -2094,7 +2094,7 @@
+ 	(void) signal(SIGCHLD, reapchild);	/* reset signal handler -ASP */
+ 	wait ((int *)0);
+ #else
+-	union wait status;
++	int status;
+ 
+ 	while (wait3(&status, WNOHANG, (struct rusage *) NULL) > 0)
+ 		;