Add some way of testing the all-in-one build scripts for dependencies

[rdw-software]

Currently, the build workflows run each individual build script (one per dependency) for more useful feedback in the UI. The problem with this approach is that the more convenient "all-in-one" build scripts (e.g., unixbuild-all.sh) aren't tested ever. I don't want to have just a single "build dependencies" step since that will be more difficult to troubleshoot in case of errors.

So I guess, an alternative solution would be to add some "unit tests" that simply check whether all files in the deps folder matching the respective naming scheme (name-unixbuild.sh or name-windowsbuild.sh) are actually called by the main script, but I don't like that either.