[llvm] [CMake] Provide `zstd::libzstd` target in `Findzstd.cmake` (PR #216968)

[Michał Górny via llvm-commits]

https://github.com/mgorny requested changes to this pull request.

Okay, so this definitely can't land as-is. The bare minimum is a comment actually explaining why it's necessary, and how to reproduce.

Judging by #139666, it happens only when you're building zstd with CMake. Linking to the bug would also be good.

That said, that bug has another suggestion which makes more sense to me. After all, it looks like you're piling a workaround on top of a workaround rather than fixing the root issue.

https://github.com/llvm/llvm-project/pull/216968