file(DOWNLOAD <url> <file> [<options>...])
file(UPLOAD <file> <url> [<options>...])
The DOWNLOAD mode downloads the given <url> to a local <file>.
If you really think this is a good idea (and you aren't just trolling),
I suppose it could be done.

 I don't think it's a good idea, but if Horizon uses cmake as its build
system, then it's way beyond that already - so you might as well do it,
it would at least prevent duplication of sources.