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

[via cfe-commits]

hstk30-hw wrote:

For now, 
empty record with size <= 64, still use `i8` in IR (before empty record without align always use `i8`), and lowering to a general purpose register.
empty record with size <= 128, use `i128` in IR, and lowering to two gr-registers (C.10).
empty record with size > 128, pass `ptr` and the val is stored on stack.



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