Add LLVM-13 installation to Docker setup (#9498)
Add LLVM-13 installation to Docker setup (#9498)

* Installs LLVM 13 in for Ubuntu 18.04 Docker images
 * This is needed as a requirement for #9425
Laurawly/tvm-1,dmlc/tvm,Laurawly/tvm-1,dmlc/tvm,Laurawly/tvm-1,Laurawly/tvm-1,Laurawly/tvm-1,dmlc/tvm,dmlc/tvm,Laurawly/tvm-1,Laurawly/tvm-1,dmlc/tvm,dmlc/tvm,Laurawly/tvm-1,dmlc/tvm,dmlc/tvm,dmlc/tvm,Laurawly/tvm-1,Laurawly/tvm-1