Hadrian: Windows build fails when creating symlink

Windows doesn't support symlinks (at least not without some extra configuration by the user https://www.joshkel.com/2018/01/18/symlinks-in-windows/). This leads to a failed windows build: https://gitlab.haskell.org/DavidEichmann/ghc/-/jobs/92823. I suggest changing the Hadrian.Utilities.createFileLink function to copy instead of link on windows (and perhaps rename the function to createFileLinkOrCopy.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information