With sources updated on Wed Jul 1 14:05:15 UTC 2020, and with a completely empty $OBJDIR and $DESTDIR, I got the following error:
... depend ===> etc/amd64/kmod nbmake[4]: nbmake[4]: don't know how to make miniroot.kmod.c. Stop nbmake[4]: stopped in $SRCDIR/distrib/amd64/kmod +--------------------+--------------------------+-----------------------+ | Paul Goyette | PGP Key fingerprint: | E-mail addresses: | | (Retired) | FA29 0E3B 35AF E8AE 6651 | p...@whooppee.com | | Software Developer | 0786 F758 55DE 53BA 7731 | pgoye...@netbsd.org | +--------------------+--------------------------+-----------------------+