[clang] Reland [C++20] [Modules] [Itanium ABI] Generate the vtable in the mod… (PR #102287)

[Matheus Izvekov via cfe-commits]

================
@@ -5163,6 +5168,13 @@ void ASTWriter::PrepareWritingSpecialDecls(Sema &SemaRef) {
   // Write all of the DeclsToCheckForDeferredDiags.
   for (auto *D : SemaRef.DeclsToCheckForDeferredDiags)
     GetDeclRef(D);
+
+  // Write all classes need to emit the vtable definitions if required.
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mizvekov wrote:

```suggestion
  // Write all classes that need to emit the vtable definitions, if required.
```

https://github.com/llvm/llvm-project/pull/102287