I’m trying to search for that “my” folder (this string i passed to package-path), but cannot find them in repo.
That was the problem, that there was no such folder, and you passed it to package path.
Download the linux version of the package (“clang+llvm-9.0.0-x86_64-linux-gnu-ubuntu-16.04.tar.xz”) and put it in the local folder (create this folder yourself): defold/local_sdks.
Then run the command:
$ ./scripts/build.py install_ext --platform=x86_64-linux --package-path=./local_sdks