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

[John McCall via cfe-commits]

rjmccall wrote:

Oh, the [Apple AArch64 calling convention](https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Pass-arguments-to-functions-correctly) diverges from AAPCS and ignores empty classes as parameters.  We appear to consider this an empty class regardless of alignment, which as discussed I believe is correct.  So Apple does not want this change on either level: we do not want our ABI to change, and we should not be considering this an empty class.

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