[llvm] [TableGen] Emit better error message for duplicate Subtarget features. (PR #102090)

[Rahul Joshi via llvm-commits]

jurahul wrote:

Thanks @nikic and @tmatheson-arm . Can you or @tmatheson-arm help merge this PR? Also, can you please choose my NVIDIA email address rjoshi at nvidia.com when merging this PR? Thanks much!

https://github.com/llvm/llvm-project/pull/102090