macOS Clang C++17 filesystem header not found

Question

I need to write a program using the (experimental) C++17 filesystem library but clang on my Mac (macOS 10.12.03) doesn\'t seem to

Answer 1

I installed XCode 9.4 - no

But Homebrew came to the rescue with LLVM 6

brew update
brew install llvm

And with a change in PATH, I was away.