[clang-tools-extra] [clang-doc] [test] Generalize error message patterns (PR #142373)

[Samarth Narang via cfe-commits]

https://github.com/snarang181 commented:

Looks fine. But I see your point regarding portability, I'll think how we can modify this. 

https://github.com/llvm/llvm-project/pull/142373