Hi, this is an issue with current develop,one of the change in the last few days do not work with recent versions of clang, I think this one might be causing it: Adds Serializer and virtual functions for new transform inits by SteveBronder · Pull Request #3019 · stan-dev/stan · GitHub
We are working on fixing it.
Our tests run with various versions of g++ and with clang+±6.0.