This is the demo for my CppCon 2019 talk! I'll update with a link to the video when it is live.
Thing should work, but it's still very much alpha demoware. Go to https://binji.github.io/wasm-clang to see it in action.
Most of the JavaScript code can be found here. If you're interested in the implementation of the in-memory filesystem, take a look at https://github.com/binji/llvm-project/tree/master/binji.