weston-launch: Add sysmacros.h include for major()

Same as with c4d7f66c, but I hadn't done a full-tree rebuild so didn't
see this one go by.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/weston-launch.c

@@ -42,6 +42,7 @@
 #include <sys/wait.h>
 #include <sys/socket.h>
 #include <sys/signalfd.h>
+#include <sys/sysmacros.h>
 #include <signal.h>
 #include <unistd.h>
 #include <fcntl.h>