Check _cffi_backend on Windows, and update translator/c/src/libffi_msvc from
hg/cffi. Notably, I think the ABI auto-detection is not working with the JIT: a
call to either a stdcall ABI function (or maybe it is a cdecl ABI function)
would work fine only in interpreter mode and crash when JITted. There is an XXX
about that in module/_cffi_backend/ctypefunc.py but the problem is not there.