LLVM Tutorial
brew install llvm@5ln -s /usr/local/Cellar/llvm@5/5.0.1/bin/llvm-config /usr/local/bin/llvm-config
brew install llvm@5
ln -s /usr/local/Cellar/llvm@5/5.0.1/bin/llvm-config /usr/local/bin/llvm-config