[clang] [llvm] [clang][LLVM Demangler] Add a diagnostic that validates that all mang… (PR #111391)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Close for me, jsut a couple of small requests.

Thanks for your patience on this response, I've been at LLVMDev all week.

https://github.com/llvm/llvm-project/pull/111391