[clang] [CIR] Record how far a bit-field's declared types reach on x86_64 (PR #220069)

[Adam Smith via cfe-commits]

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@@ -79,6 +79,24 @@ struct CIRRecordLowering final {
         cir::ArrayType::get(cirGenTypes.convertTypeForMem(field->getType()), 0),
         cir::RecordMemberKind::BitField);
   }
+
+  /// A member recording that declared types reach \p excessInBits past where
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adams381 wrote:

I've rewritten the entire comment block to try and be more clear.

https://github.com/llvm/llvm-project/pull/220069