>I also put a tarfile of as86/ld86 from a nearby linux system into
>ftp://sipb.mit.edu/pub/netbsd/dosemu/as-ld-86.tar.gz

Please use a current version from
somewhere/FreeBSD-current/ports/distfiles/bcc.tar.gz.
somewhere/FreeBSD-current/ports/devel/bcc/*

This version is slightly newer, more correctly copylefted, more
correctly configured for *BSD, and is packaged with my not-quite
K&R1 C compiler for 6809, 8086 and 80x86 targets.

Bruce