Cloning repo
$ git clone https://github.com/llvm/clangir.git llvm-project
Adding remote
Alternatively, one can just add remotes:
$ cd llvm-project
$ git remote add llvm-clangir git@github.com:llvm/clangir.git
$ git fetch llvm-clangir
$ git checkout -b clangir llvm-clangir/main