Now that VS2015 update 3 is officially released (no longer RC 3), it completely breaks UE 4.12! Everything was fine before installing Update 3. And yes Update 3 will remove some of the C++ features that you may have had installed before the update. I did notice that C++ was missing after the update. But even after reinstalling the C++ features, VS2015 update 3 still does not build UE4.12. But I was able to find a workaround, that works
- run the command
GenerateProjectFiles.bat -2013
- open the project with VS2013
- rebuild