'cd /usr/src/etc; make distribute' broken.

As part of my world-building script for creating binary distributions
for use on bento I use the following to populate /etc in the target
directory:
---
cd /usr/src/etc
make distribute DISTRIBUTION=/destdir TARGET_ARCH=whatever
---
This used to work fine, but now it is dying with the following:

install -o root -g wheel -m 644  /a/asami/portbuild/amd64/5/src/etc/sendmail/freebsd.mc /a/asami/portbuild/amd64/5/src/etc/sendmail/freebsd.cf //var/chroot/etc/mail
install: /a/asami/portbuild/amd64/5/src/etc/sendmail/freebsd.cf: No such file or directory
*** Error code 71

Stop in /a/asami/portbuild/amd64/5/src/etc/sendmail.
*** Error code 1

Indeed, freebsd.cf does not appear to be built anywhere.  Does anyone
know what is going on?

Kris