In principle, major FreeBSD versions should be ABI compatible.
But in this case the python3 binary would only run on 13.1, not 13.0.

Signed-off-by: falkTX <falktx@falktx.com>

Signed-off-by: falkTX <falktx@falktx.com>

Apparently the ${HOME} variable is set to the filesystem root "/" in
Cirrus CI FreeBSD instances. Just create an installation directory
without it, then.

While here, set --pkgconfigdir to closely mimick the build in the
FreeBSD ports tree.

When the github application Cirrus CI (https://cirrus-ci.org/) is
installed, this build description file adds FreeBSD build checks to
changes and PRs in github.

There are four build tasks currently, a minimal build and one with all
options enabled on two different FreeBSD versions.