Just a heads up, in case you are asked if you want to install updates on your Mac build server today. I'm having problems after the update. It's probably something daft that I was supposed to do, but just in case.
Details at:
Note that whilst typing this, another popup has appeared, asking if I want to apply more updates to XCode. I'll give it a go and see what happens. Wish me luck...
After next set of updates, I now hit the same problem as many other people, Details at https://forums.xamarin.com/discussion/51100/ios-linker-error-cant-not-find-the-nested-type-when-built-in-visual-studio-but-not-xamarin-studio
Now cannot build iOS from VS at all.