[clang] [CodeGen][CIR] Split out Backend Diags to utils, impl CIR error-attr (PR #225966)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > Sorry for the mistaken ping, @arsenm. The CIR-to-LLVM IR lowering changes look good to me. One small test typo: the WARN check says pelase, but the attribute message says please, at `clang/test/CIR/Diagnostics/attr-error.c` L14
> 
> Uhhh what the heck! I coulda sworn that worked! Is it self matching or something?!?! I'll have to look at this again when I get to work monday.

Thats exactly what it was actually!  When I was messing with this, it wasn't actually printing the line, so the check lines were failing correctly.   But once it errored/printed the right line, it was printing the WHOLE line, which included the comment :D 

https://github.com/llvm/llvm-project/pull/225966