the README of src/tools/tools mentions the recoverdisk which has already been moved to /sbin, so please remove this line: https://github.com/freebsd/freebsd/blob/master/tools/tools/README#L58
A commit references this bug: Author: emaste Date: Wed Apr 18 14:02:37 UTC 2018 New revision: 332673 URL: https://svnweb.freebsd.org/changeset/base/332673 Log: Remove mention of tools/recoverdisk, now in sbin PR: 227570 MFC after: 3 days Changes: head/tools/tools/README
A commit references this bug: Author: emaste Date: Sat Apr 21 00:27:35 UTC 2018 New revision: 332848 URL: https://svnweb.freebsd.org/changeset/base/332848 Log: MFC r332673: Remove mention of tools/recoverdisk, now in sbin PR: 227570 Changes: _U stable/11/ stable/11/tools/tools/README