[build system] Using External Modules - Breaking Change

Hi there,

is anyone using external modules? I have opened a pull request (as of now still work in progress) that would change the behavior in a breaking way.

It would technically be possible to keep the current behavior while introducing the new behavior using a different variable and then go through the usual deprecation process. However, I believe that there are few external users for this feature and those would likely directly jump on the behavior, so that no deprecation is needed - especially since the new approach fixes bugs. Migration is done in less than a minute. All details are given in the PR.

So: If you are using external modules, it would be super nice if you could give feedback on whether you need a deprecation period or not.