For OSX, this requires llvm-ar at the following path:
/usr/local/opt/llvm/bin/llvm-ar
This can be installed via Brew, aka brew install llvm.
Then, download, install and activate the Emscripten SDK:
./emsdk/emsdk install latest
./emsdk/emsdk activate latest
source emsdk/emsdk_env.sh
Then perform build by running:
make