autoreconf not installing config.sub/.guess

I see from the release notes that autoconf 2.69d installs
config.guess/config.sub automatically now. This is good news for us as
we've got patches to autoreconf to run 'gnuconfigize' which copies
into the source tree the latest config.* files, and hopefully we can
drop this now.

I tried, however, and Berkeley DB failed to build:

| checking build system type... Invalid configuration `aarch64-linux':
machine `aarch64' not recognized
| configure: error: /bin/bash ../db-5.3.28/dist/config.sub aarch64-linux failed

That file is indeed the original config.sub from 2011 still.  We run
autoreconf --install --force so was expecting these files to be
overwritten.

Ideas?

Thanks,
Ross