[clang] [clang][Modules] Fix the Size of `RecordDecl`'s `BitCodeAbbrevOp` (PR #133500)

[Qiongsi Wu via cfe-commits]

https://github.com/qiongsiwu created https://github.com/llvm/llvm-project/pull/133500

https://github.com/llvm/llvm-project/pull/102040/files#diff-125f472e690aa3d973bc42aa3c5d580226c5c47661551aca2889f960681aa64dR2477 added 1 bit to `RecordDecl`'s serialization format, but did not increment its abbreviation size. 

This can lead to rare cases where a record may overflow if a `RecordDecl`'s `getArgPassingRestrictions()` returns something bigger than 1 (see [here](https://github.com/llvm/llvm-project/blob/b3f01a6aa45b00240cec1c64286b85d7ba87e2af/clang/lib/Serialization/ASTWriterDecl.cpp#L688)). 

>From ced1940dc432f518edb86d7af24f614ecf341b82 Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu at apple.com>
Date: Fri, 28 Mar 2025 09:56:36 -0700
Subject: [PATCH] Fixing RecordDecl's abbreviation's size.

---
 clang/lib/Serialization/ASTWriterDecl.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Serialization/ASTWriterDecl.cpp b/clang/lib/Serialization/ASTWriterDecl.cpp
index a14b8cf201bba..f377c145a4204 100644
--- a/clang/lib/Serialization/ASTWriterDecl.cpp
+++ b/clang/lib/Serialization/ASTWriterDecl.cpp
@@ -2579,7 +2579,7 @@ void ASTWriter::WriteDeclAbbrevs() {
   // RecordDecl
   Abv->Add(BitCodeAbbrevOp(
       BitCodeAbbrevOp::Fixed,
-      13)); // Packed Record Decl Bits: FlexibleArrayMember,
+      14)); // Packed Record Decl Bits: FlexibleArrayMember,
             // AnonymousStructUnion, hasObjectMember, hasVolatileMember,
             // isNonTrivialToPrimitiveDefaultInitialize,
             // isNonTrivialToPrimitiveCopy, isNonTrivialToPrimitiveDestroy,