Building emscripten is done by:
https://kripken.github.io/emscripten-site/docs/getting_started/Tutorial.html
git clone https://github.com/juj/emsdk.git
cd emsdk
./emsdk update
./emsdk install latest
./emsdk activate latest
echo "source ./emsdk_env.sh" >> ~/.bash_profile
building hello.wasm (666 bytes). pretty cool asm code run by your browser :) weeee... this is fun and useful for more nefarious things.
hex dump