The VST, VST3, & AU wrappers, as well as several CoreAudioUtilityClasses files, all include CSCommon.h from the OS X 10.11 SDK's Security.framework and it seems to have a problem with "1<<31" being used or something of that sort..
Someone else reported this too, but it seems to just be because the bleeding-edge version of Clang that we have to use has added new error detection, and is flagging up this (perfectly sensible) error.
Presumably when Apple catch up to their own Clang changes, they'll also update this header, but we'll have a look and see if we can do anything to stop it happening.