[clang] [RFC][clang] Handle friend function that was a definition but became only a declaration during AST deserialization (PR #132214)

[Chuanqi Xu via cfe-commits]

================
@@ -1390,7 +1390,19 @@ class ASTReader
   /// predefines buffer may contain additional definitions.
   std::string SuggestedPredefines;
 
-  llvm::DenseMap<const Decl *, bool> DefinitionSource;
+  struct DefinitionSourceFlags {
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ChuanqiXu9 wrote:

```suggestion
  struct DefinitionSourceBits {
```

nit: Personal taste

https://github.com/llvm/llvm-project/pull/132214