[clang] [clang][Sema] Merge GNU diagnostic attributes by semantic spelling (PR #214523)

[Shengxin Pei via cfe-commits]

TPPPP72 wrote:

I think all these [PR](https://github.com/matthiasgoergens/llvm-project/pull) were generated by LLMs.

https://github.com/llvm/llvm-project/pull/214523