As I test this myself, I found that it’s not that easy (each compiler upgrade comes with a new set of restrictions I have to work through).
Use the currently used version instead, and everything should work as intended.
https://releases.llvm.org/9.0.0/clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz
I have updated the readme with this link.