[clang] [NFC] [Serializer] Pack information in serializer (PR #69287)

[Vassil Vassilev via cfe-commits]

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@@ -1689,9 +1709,10 @@ void ASTDeclReader::VisitParmVarDecl(ParmVarDecl *PD) {
   } else {
     PD->setScopeInfo(scopeDepth, scopeIndex);
   }
-  PD->ParmVarDeclBits.IsKNRPromoted = Record.readInt();
-  PD->ParmVarDeclBits.HasInheritedDefaultArg = Record.readInt();
-  if (Record.readInt()) // hasUninstantiatedDefaultArg.
+  PD->ParmVarDeclBits.IsKNRPromoted = ParmVarDeclBits.getNextBit();
+  ;
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vgvassilev wrote:

```suggestion
```

https://github.com/llvm/llvm-project/pull/69287