The error pretty much says it all, that the path “my/clang%2Bllvm-9.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz” is an invalid url.
Do you have the external packages in a folder locally?
You can read more about the “–package-path” here:
And the SDK package scripts are located under “./scripts/package/*”
Although I see now that we have no package script for clang.
You can download it from here:
http://releases.llvm.org/download.html