Message 271919 - Python tracker

I've uploaded a new patch which adds a test. I've confirmed that *without* the patch to Modules/_ctypes/libffi_msvc/ffi.c, the test passes on win32 and fails on amd64. *With* the patch to Modules/_ctypes/libffi_msvc/ffi.c, the test passes on both win32 and amd64.

I'll apply this patch if I don't hear any objections or suggested improvements before Friday 2016-08-05.