On the latest macOS, just type clang on your terminal and a dialog would appear if you don't have clang compiler. Follow the instruction to install it.
You might find the following error when executing clang.
xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun
In this case, run xcode-select --install and install commandline tools.