[clang] [Clang][Cygwin] Link default-manifest.o if exists (PR #220875)

[Christoph Reiter via cfe-commits]

lazka wrote:

> > If we want to do the same for MinGW, I'm happy to make a PR for that.
> 
> I think that might be useful, or what do @lazka and @lhmouse think?

Yes, I think it would be helpful. Reducing the diff to gcc, and providing a better out of the box experience without having to deal with manifests. For context, this is what is currently used: https://sourceware.org/git/?p=cygwin-apps/windows-default-manifest.git;a=blob;f=default-manifest.rc;h=2c4ddf4783b953afaf7df9473450bf95842d1911;hb=HEAD

https://github.com/llvm/llvm-project/pull/220875