Add new port devel/aunit
This is a test dependency of the upcoming AdaID port. There are existing ports that also could use Aunit but they currently work around or skip testing options. === AUnit is a set of Ada packages based on the xUnit family of unit test frameworks. It is intended as a developer's tool to facilitate confident writing and evolution of Ada software. It is purposely lightweight, as one of its main goals is to make it easy to develop and run unit tests, rather than to generate artifacts for process management. The framework supports easy composition of sets of unit tests to provide flexibility in determining what tests to run for a given purpose.