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

[Viktoriia Bakalova via cfe-commits]

VitaNuo wrote:

> Thanks! I thought i commented elsewhere, but I think `diagnose` vs `diagnostics` for the flags/etc makes more sense: `fdiagnostics_demangler_failures` should be `-fdiagnose_demangler_failures`, it is the correct language-tense.

Thanks! I think it was `demangling` vs. `demangler`, and now it's `diagnostics` vs. `diagnose` :) I'll incorporate that.

> Else, the patch is good delta what happens with the RFC. Please make sure to wait until Aaron calls the RFC.

Ofc. I am also OOO next week.


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