They are identical copies of each other. Since symlink support is not universal on Windows (Possible since around the time WSL was introduced, but still requires either special privileges or developer mode enabled), many tools including GNU autotools fall back to copying. Since recently (https://reviews.llvm.org/D99170), LLVM et least tries to create a symlink on Windows, but still caused problems because this is kind of unexpected by Windows. The NSIS installer used by the official Windows installer (https://llvm.org/builds/) does not support symlinks at all such that the installer includes 4 identical copies of Clang.
A clean solution would be to have stub executables that link to a central libClang.dll/libLLVM.dll (-DCLANG_LINK_CLANG_DYLIB=ON), but this is not supported under Windows because a DLL can export at most 2^16 symbols. Some work would need to be invested to make process launching on Windows work differently than on other platforms, but then disk space is not that much of a problem.
A clean solution would be to have stub executables that link to a central libClang.dll/libLLVM.dll (-DCLANG_LINK_CLANG_DYLIB=ON), but this is not supported under Windows because a DLL can export at most 2^16 symbols. Some work would need to be invested to make process launching on Windows work differently than on other platforms, but then disk space is not that much of a problem.