[clang] [Modules] Fix the inconsistency of which `Decl` should be serialized for an identifier. (PR #135887)

[Volodymyr Sapsai via cfe-commits]

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@@ -224,6 +224,7 @@ class ASTWriter : public ASTDeserializationListener,
   /// discovery) and start at 2. 1 is reserved for the translation
   /// unit, while 0 is reserved for NULL.
   llvm::DenseMap<const Decl *, LocalDeclID> DeclIDs;
+  // TMP: ^ DeclIDs type for reference
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vsapsai wrote:

I will remove all TMP comments before committing. Using this to simplify the review by pulling in the pointers to the relevant code.

https://github.com/llvm/llvm-project/pull/135887