This is currently just a light SHA update of the current llvm formula, which is at
3.8.1. Not surprisingly it ends up looking a lot like Godin's update of llvm to 3.9.0
here: Homebrew/homebrew-core#4579 . LLVM switched to CMake-based
builds after 3.8. This is why I haven't adapted the current llvm38 formula
because it (probably) requires a good bit of changing to move it over from autoconfig.
brew install llvm39builds to completion - see _latest_build.txt- creates /usr/local/opt/llvm39 directory as a symlink to /usr/local/Cellar/llvm39/3.9.0/
brew test llvm39fails on the first C++ build with problems finding stdarg.h - see _test_failure.txt