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

[Dmitry Polukhin 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 {
+    ExtKind HasExternalDefinitions : 2;
+
+    /// Indicates if given function declaration was a definition but its body
+    /// was removed due to declaration merging.
+    bool ThisDeclarationWasADefinition : 1;
+
+    DefinitionSourceFlags()
+        : HasExternalDefinitions(EK_ReplyHazy),
+          ThisDeclarationWasADefinition(false) {}
+  };
+
+  llvm::DenseMap<const Decl *, DefinitionSourceFlags> DefinitionSource;
----------------
dmpolukhin wrote:

I think memory overhead for another map will be higher. The value_type was bool but in reality at least 4-8 bytes were allocated for it so converting it to struct with 3 bits only shouldn't take extra space.

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