sysutils/immortal: Unbreak build on arm64

./scandir.go:69:5: undefined: WatchDir
./scandir.go:72:5: undefined: WatchDir
./scandir.go:172:12: undefined: WatchFile
./scandir.go:176:11: undefined: WatchFile
./supervise.go:158:12: s.daemon.WatchPid undefined (type *Daemon has no field or method WatchPid)

http://thunderx1.nyi.freebsd.org/data/head-arm64-default/p518178_s355024/logs/errors/immortal-0.24.0.log

https://github.com/immortal/immortal/pull/55

PR: 242312