If Amazon/EC2 is still based on CentOS/Fedora, maybe you could try something like this:

$ echo 'HOME_DIR=/home/$(whoami)' >> .bashrc; source .bashrc ; curl -O http://releases.llvm.org/4.0.1/clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25.tar.xz; tar xvf clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25.tar.xz; echo 'export PATH=$HOME_DIR/clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25:$PATH' >> .bashrc; source .bashrc; cd ~

OR

$ echo 'HOME_DIR=/home/$(whoami)' >> .bashrc
$ source .bashrc
$ curl -O http://releases.llvm.org/4.0.1/clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25.tar.xz
$ tar xvf clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25.tar.xz
$ echo 'export PATH=$HOME_DIR/clang+llvm-4.0.1-x86_64-linux-gnu-Fedora-25:$PATH' >> .bashrc
$ source .bashrc
$ cd ~