Hello swift-dev!
We are going to be performing an update to the llvm/clang stable branches within the next couple of days. I will send out an email before I pull the trigger. We will be using a -s ours merge so if you run update-checkout (or even just git pull), everything should fast forward appropriately.
If you have any questions, please feel free to send me an email (or respond to this one).
Thanks,
Michael