32-bit msvc variadic FFI probably broken

[retep998]

https://ci.appveyor.com/project/GuillaumeGomez/va-list-rs/build/1.0.22

Only the 32-bit msvc tests are failing. After adding some debug printfs to the C code it appears that the arguments are busted as soon as create_va_list is called. I even tacked on some __cdecl to make sure it wasn't accidentally compiling the function with the wrong calling convention.

Due to #32305 this was never caught otherwise.

[GuillaumeGomez]

cc me

[retep998]

Nevermind, it seems va_start was just being called with an incorrect second parameter, which somehow only 32-bit msvc cared about.