This is a follow-up to D65109 which removes the Xcode project. It seems that the script to generate the Xcode project was the most controversial, so I've split it off into a separate review.
From the original patch:
I created a new script to streamline the process: it creates two build directories in the current directory. The first directory is for LLVM and Clang which uses Ninja to build. The second directory is for LLBD, which configures a standalone build using the Xcode generator.