mesa-dev.tcz Depends on Missing llvm19-dev.tcz

[CNK]

In TC17 x86_64, mesa-dev.tcz.dep contains "llvm19-dev.tcz" but this extension is no longer available (replaced by "llvm22-dev.tcz").

[Juanito]

I've been wondering about the best way to do this for a while now.

What we don't want is for maintainers to use obsolete extensions to build new extensions, hence the removal of llvm19-dev, but I agree this breaks *dev extensions that rely on it until such point that they too are updated.