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

[via cfe-commits]

jeremyd2019 wrote:

By simply removing `AND NOT CYGWIN` from https://github.com/llvm/llvm-project/blob/6fc3b40b2cfc33550dd489072c01ffab16535840/llvm/cmake/modules/AddLLVM.cmake#L753

```
usr/bin/cygLLVM.dll -> cygLLVM-20.dll
usr/bin/cygLLVM-20.1.8.dll -> cygLLVM-20.dll
usr/bin/cygLLVM-20.dll
```

Apparently that symlink making part only gets turned on if llvm_add_library gets an `SONAME` argument, I expected this to happen with the clang libraries too...

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