[clang] [clang-tools-extra] [clang] Refactor `clang::Linkage` (PR #71049)

[Chuanqi Xu via cfe-commits]

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@@ -2214,7 +2214,7 @@ void ASTWriter::WriteDeclAbbrevs() {
   Abv->Add(BitCodeAbbrevOp(0));                       // TSCSpec
   Abv->Add(BitCodeAbbrevOp(0));                       // InitStyle
   Abv->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // isARCPseudoStrong
-  Abv->Add(BitCodeAbbrevOp(0));                       // Linkage
+  Abv->Add(BitCodeAbbrevOp(1));                         // Linkage
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ChuanqiXu9 wrote:

> If I guess correctly that this value corresponds to Linkage::None we have in some default constructors, we should consider changing that default to Linkage::Invalid.

No. It is not the case. Sorry for didn't explaining things clearly. The value here means the linkage for ParmVarDecl according to line [2185](https://github.com/llvm/llvm-project/pull/71049/files#diff-125f472e690aa3d973bc42aa3c5d580226c5c47661551aca2889f960681aa64dR2185). So it is natural that ParmVarDecl doesn't have a linkage.

https://github.com/llvm/llvm-project/pull/71049