It's worth mentioning that the "vivid universe" is in fact a dev branch, Vivid Vervet (ubuntu 15.04).
I also updated clang to 3.6 and it pulled the whole world in! I rebooted and I'm now facing "Ubuntu Vivid Vervet (development branch)" which wasn't my intention, as I meant to stay on LTS.
I'm officially bleeding edge :(
So, word of warning, if you're on 14.04 LTS and just want to build vibe.d with GDC, upgrade only GDC to 4.9.2 from the vivid universe. Don't touch anything else and revert your repos to "trusty" after pulling in GDC 4.9.2