[clang] fix: compatible C++ empty record with align UB with gcc (PR #72197)

[Eli Friedman via cfe-commits]

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@@ -307,7 +307,13 @@ AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadic,
     // 0.
     if (IsEmpty && Size == 0)
       return ABIArgInfo::getIgnore();
-    return ABIArgInfo::getDirect(llvm::Type::getInt8Ty(getVMContext()));
+    // An empty struct can have size greater than one byte if alignment is
+    // involved.
+    // When size <= 64, we still hold it by i8 in IR for compatible,
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efriedma-quic wrote:

For compatibility with what?

https://github.com/llvm/llvm-project/pull/72197