[clang] [ARM] Empty structs are 1-byte for C++ ABI (PR #124762)

[Eli Friedman via cfe-commits]

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@@ -1144,6 +1144,12 @@ Arm and AArch64 Support
 
   * FUJITSU-MONAKA (fujitsu-monaka)
 
+- The AArch64 calling convention for empty structs in C++ mode was changed to
+  pass them as if they have a size of 1 byte, matching the AAPCS64
+  specification and GCC's implementation. The previous behaviour of ignoring
+  the argument can be restored using the -fclang-abi-compat=20 (or earlier)
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efriedma-quic wrote:

20?  You're not planning to cherry-pick this to the release branch?

https://github.com/llvm/llvm-project/pull/124762