[llvm] [IRLinker] Don't add duplicate named MD node operand to dest module (PR #146020)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> Unfortunately, this problem is not unique to AMDGPU target. Do you think we should make unify-metadata pass target independent and run it for other targets as well (e.g. SPIR-V)?

The pass is garbage, the linker should be doing this. A follow up patch should delete it. IMO nobody is ever going to do the suggested work of making uniquability a configurable property for named metadata 

https://github.com/llvm/llvm-project/pull/146020