[clang] [C++20][Modules] Allow using stdarg.h with header units (PR #100739)

[Chuanqi Xu via cfe-commits]

================
@@ -4543,7 +4544,7 @@ ASTReader::ASTReadResult ASTReader::ReadAST(StringRef FileName, ModuleKind Type,
 
       // Mark this identifier as being from an AST file so that we can track
       // whether we need to serialize it.
-      markIdentifierFromAST(*this, *II);
+      markIdentifierFromAST(*this, *II, true);
----------------
ChuanqiXu9 wrote:

```suggestion
      markIdentifierFromAST(*this, *II, /*IsModule=*/true);
```

https://github.com/llvm/llvm-project/pull/100739