[llvm] [TableGen] Rework error reporting for duplicate Feature/Processor. (PR #102257)

[Rahul Joshi via llvm-commits]

jurahul wrote:

> Yes, and hopefully it will report the "correct" location for the multiclass example, too.

Let me try. That seems easier and cheaper than extracting the info from SMLoc.

https://github.com/llvm/llvm-project/pull/102257