Continuous “Platform” Integration?

Question

We have accumulated a large codebase of somewhat-well-document projects, many of which aren't actively being used, but that we want to be able to start using again quickly if necessary.

What is the best way to automatically make sure that these projects stay in working condition as the dependencies backing different projects are upgraded?

These dependencies tend to be large, open-source and external, such as OpenCV and FFMPEG.

Between consecutive versions, they offer Warnings during compilation about the use of recently-deprecated functions; jump more than a few version, though, and updating becomes a significantly more challenging task.