The repository should be cloned to the AvA root directory. In this directory:

mkdir build
cd build
cmake -DLLVM_ENABLE_PROJECTS=clang -G "Unix Makefiles" ../llvm
make

or simply execute:

./scripts/build.sh

This will place the build artifacts in llvm/build. You do not need to install them. nwcc (CAvA) will find them in their build locations.

Install docker and run this script to build LLVM in a container:

./scripts/build_release.sh

Then the tarball will be copied to ${PWD}/artifacts. To use the binary for AvA, simply unpack the tarball in ${AVA_ROOT}/llvm.