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

[Aaron Ballman 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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AaronBallman wrote:

Agreed that those should be swapped to `Invalid` instead of `None` (better done as a separate follow-up patch as it isn't an NFC change). However, this is a change to the serialization format so a new PCH consumed by an older Clang will misbehave. Please check whether `VERSION_MAJOR` (in `ASTBitCodes.h`) has been updated for this release and if it hasn't been, increment it by one.

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