You could nuke the whole thing and start over, by just following Andrew’s link, that would always be the safe thing to do. I suppose your question is: Do I have to do that or is there a safe way to just get the updates from the branch and building again?
I think the following is pretty safe (I did it a couple of days ago myself):
git checkout v0.6
git submodule update --init --recursive
On Windows and Linux you can add
-j$(nproc) right after make for performance, and on Mac it’s
-j$(sysctl -n hw.ncpu) instead.