[clang] fix: C++ empty record with align lead to va_list out of sync (PR #72197)

[Eli Friedman via cfe-commits]

================
@@ -110,6 +110,9 @@ C++ Specific Potentially Breaking Changes
 ABI Changes in This Version
 ---------------------------
 
+- Let C++ empty record fall through to the standard argument-handling path instead of
+  always pass a single ``i8`` according to aarch64 AAPCS rules.
----------------
efriedma-quic wrote:

Maybe tweak the release note a little; the reference to `i8` doesn't really make sense from the perspective of a clang user.

```suggestion
- Fix AArch64 argument passing for C++ empty classes with large explicitly specified
  alignment.
```

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