https://bugs.winehq.org/show_bug.cgi?id=48442
--- Comment #13 from Esme Povirk madewokherd@gmail.com ---
From compiling a test program and looking at disassembly, it seems like va_list
on Windows is just a pointer to a buffer containing the arguments. That leaves a lot of ambiguity in terms of how things are packed, but in most cases they're likely to be pointer-sized.