QEMU cirrus freebsd 13 CI failing with 'Undefined symbol "rl_set_timeout"'

[Peter Maydell <peter.maydell@linaro.org>]

I've just noticed that our (optional) FreeBSD 13 CI job is
failing while running the qemu-iotests, like this:

+ld-elf.so.1: /usr/local/bin/bash: Undefined symbol "rl_set_timeout"

Full job logs from a couple of sample builds:
https://cirrus-ci.com/task/6541458329567232
https://cirrus-ci.com/task/6036627739377664

Any idea what this is about? It looks at first glance like
the bash on the CI system is busted because it can't find
libreadline, but maybe I'm missing something. Are we missing
some runtime shared library from a config file?

(I didn't notice this immediately because our 'make check'
logging is so voluminous that gitlab truncates it, so you
have to click through to the gitlab job log, find the cirrus
URL, then go look at it in Cirrus. We still really need to
trim down the amount of output we're emitting here.)

thanks
-- PMM