[clang] [clang][ItaniumMangle] Fix mangling of lambdas in default member initializers of local classes (PR #206740)

[Erich Keane via cfe-commits]

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@@ -1945,8 +1944,13 @@ void CXXNameMangler::mangleLocalName(GlobalDecl GD,
       mangleUnqualifiedBlock(BD);
     } else {
       const NamedDecl *ND = cast<NamedDecl>(D);
-      mangleNestedName(GD, Context.getEffectiveDeclContext(ND),
-                       AdditionalAbiTags, true /*NoFunction*/);
+      const NamedDecl *PrefixND = getClosurePrefix(ND);
+      if (PrefixND && !isCompatibleWith(LangOptions::ClangABI::Ver18))
+        mangleNestedNameWithClosurePrefix(GD, PrefixND, AdditionalAbiTags,
+                                          true /*NoFunction*/);
+      else
+        mangleNestedName(GD, Context.getEffectiveDeclContext(ND),
+                         AdditionalAbiTags, true /*NoFunction*/);
----------------
erichkeane wrote:

```suggestion
                         AdditionalAbiTags, /*NoFunction=*/true);
```

https://github.com/llvm/llvm-project/pull/206740