On 64-bit Windows, ffi_arg must be 8 bytes long. This fixes the

remaining crashes in the ctypes tests, when functions return float or
double types.

Modules/_ctypes/libffi_msvc/ffitarget.h

@@ -36,7 +36,11 @@
 /* ---- Generic type definitions ----------------------------------------- */
 
 #ifndef LIBFFI_ASM
+#ifndef _WIN64
 typedef unsigned long          ffi_arg;
+#else
+typedef unsigned __int64       ffi_arg;
+#endif
 typedef signed long            ffi_sarg;
 
 typedef enum ffi_abi {