A recent build-report showed a problem building the vile port.
The symptom pointed to a problem with parallel make.

The likely problem seems to be as reported against the make program here:

http://gnats.netbsd.org/55542
"make: parallel builds and double-colon don't get along"

That is, double-colon targets in the makefiles cause the build to fail.
vile uses this in several places, and rewriting the makefiles to work
around a bug in a given make-program isn't going to happen.  It works
well enough with gmake, but is easy to reproduce with bmake with my
Debian/testing for instance:

--- all ---
--- bnf-filt.o ---
rm -f bnf-filt.c
--- css-filt.o ---
echo "#include <flt_defs.h>" > css-filt.c
flex -t css-filt.l >> css-filt.c
clang -c -I. -I.. -I../filters -I.. -DHAVE_CONFIG_H -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=500 -D_FILE_OFFSET_BITS=64 -I./filters -g -O2 -Qunused-arguments -Wno-error=implicit-function-declaration   css-filt.c
bmake: all#1: cohort has parents

bmake: stopped in /usr/build/vile/vile

The problem with make appears to be recent; it works with FreeBSD 12.
(I tried installing FreeBSD-13-current...).  The Debian/testing package
also is new:

https://packages.debian.org/bullseye/bmake
"bmake (20200710-5)"

The port should be updated to suppress the parallel-make feature.