[llvm] [llvm-link] Improve missing file error message (PR #82514)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Should we add something that (lit-)checks the changed error message?

If there's an existing check it may still pass since it checks the prefix. I don't think it's an issue personally.

https://github.com/llvm/llvm-project/pull/82514