This is the error I get when trying to build Boost 1.69.0 with LLVM: "error: ISO C++17 does not allow 'register' storage class specifier [-Wregister]".  I've also sent an email about this to the LLVM developer mailing list.  

I've attached the project-config.jam file to this message.  Please let me know how to fix this.  Thanks in advance.