New review comment by mvf on void-packages repository

https://github.com/void-linux/void-packages/pull/33623#discussion_r732021229

Comment:
> Could it be made a proper package we link against?

I'd prefer that too, but this would require major surgery. The SDK has no clean separation into interface and implementation and no install rules. As-is, it can pretty much only be used from source. `qtractor` directly compiles source files from the SDK directory.

> If not, can you think of a reason people would want to disable it? Simplifying dependency fetching can be worth it because it allows xgensum to actually replace the checksums cleanly for you.

Now that you mention it, there's no real reason to disable VST3. There are no downsides, and without it `qtractor` is significantly less useful. I made it a mandatory dep.