If one builds system with WITHOUT_LEGACY_CONSOLE=yes in /etc/src.conf and deletes /usr/sbin/kbdcontrol via make delete-old, new builds after 'make cleanworld' will fail during bootstrap phase of buildworld.
I can only see it being used for a few header files in the kernel? So maybe the solution is to just not add the bootstrap symlink with MK_LEGACY_CONSOLE=no?
See also: https://reviews.freebsd.org/D29200
50179c5ec7d09d7b02497caf95dca5d33f93bcd9