[clang] [clang][Itanium Mangle] Enable mangling of enclosing class for member… (PR #110503)

[Richard Smith via cfe-commits]

================
@@ -693,7 +693,7 @@ ItaniumMangleContextImpl::getEffectiveDeclContext(const Decl *D) {
     if (VD->isExternC())
       return getASTContext().getTranslationUnitDecl();
 
-  if (const auto *FD = D->getAsFunction()) {
+  if (const auto *FD = dyn_cast<FunctionDecl>(D)) {
----------------
zygoloid wrote:

Maybe we can reduce the duplication a little?
```suggestion
  if (const auto *FD = 
          getASTContext().getLangOpts().getClangABICompat() >
            LangOptions::ClangABI::Ver19 ? D->getAsFunction() : dyn_cast<FunctionDecl>(D)) {
```

https://github.com/llvm/llvm-project/pull/110503