BITS: On x86-64, add the FFI_EFI64 calling convention

As with stdcall on win32, it's the calling convention used when *not*
passing FUNCFLAG_CDECL (rather than having an explicit flag of its own).

Author: joshtriplett

Modules/_ctypes/callbacks.c

@@ -460,6 +460,9 @@ CThunkObject *_ctypes_alloc_callback(PyObject *callable,
 #if defined(MS_WIN32) && !defined(_WIN32_WCE) && !defined(MS_WIN64)
     if ((flags & FUNCFLAG_CDECL) == 0)
         cc = FFI_STDCALL;
+#elif defined(X86_64) && !defined(X86_WIN64)
+    if ((flags & FUNCFLAG_CDECL) == 0)
+        cc = FFI_EFI64;
 #endif
     result = ffi_prep_cif(&p->cif, cc,
                           Py_SAFE_DOWNCAST(nArgs, Py_ssize_t, int),

Modules/_ctypes/callproc.c

@@ -799,6 +799,9 @@ static int _call_function_pointer(int flags,
 #if defined(MS_WIN32) && !defined(MS_WIN64) && !defined(_WIN32_WCE)
     if ((flags & FUNCFLAG_CDECL) == 0)
         cc = FFI_STDCALL;
+#elif defined(X86_64) && !defined(X86_WIN64)
+    if ((flags & FUNCFLAG_CDECL) == 0)
+        cc = FFI_EFI64;
 #endif
     if (FFI_OK != ffi_prep_cif(&cif,
                                cc,