[clang] [Serialization] [ASTWriter] Try to not record namespace as much as possible (PR #179178)

[Shafik Yaghmour via cfe-commits]

================
@@ -4817,10 +4826,8 @@ void ASTWriter::GenerateNameLookupTable(
     Generator.insert(ConversionDecls.front()->getDeclName(),
                      Trait.getData(ConversionDecls), Trait);
 
-  // Create the on-disk hash table. Also emit the existing imported and
-  // merged table if there is one.
-  auto *Lookups = Chain ? Chain->getLoadedLookupTables(DC) : nullptr;
-  Generator.emit(LookupTable, Trait, Lookups ? &Lookups->Table : nullptr);
+  // Create the on-disk hash table.
+  Generator.emit(LookupTable, Trait, nullptr);
----------------
shafik wrote:

```suggestion
  Generator.emit(LookupTable, Trait, /*Base=*/nullptr);
```

https://github.com/llvm/llvm-project/pull/179178