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

[Andy Kaylor via cfe-commits]

================
@@ -1,8 +1,12 @@
 set(LLVM_LINK_COMPONENTS
+  CodeGen
----------------
andykaylor wrote:

Does make CIR CodeGen depend on classic CodeGen? Is there any way we can avoid that?

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