[clang] [libclang][Cygwin] Provide unversioned DLL file alongside versioned one (PR #147132)

[via cfe-commits]

jeremyd2019 wrote:

> a symlink alone won't suffice here, as `dlopen()` ultimately calls `LoadLibraryExW`, which does not follow Cygwin-style symlinks.

If dlopen doesn't work on a Cygwin symlink, that is a bug in dlopen and should be fixed in Cygwin.

https://github.com/llvm/llvm-project/pull/147132