[M68k] Fix empty builtin va_list kind

Clang _requires_ every target to provide a va_list kind so we shouldn't
put a llvm_unreachable there. Using `VoidPtrBuiltinVaList` because m68k
doesn't have any special ABI for variadic args.

GitOrigin-RevId: 59437cb7d7c30054f0e77b2369c0aeffed3ccb14
1 file changed