use enums mp_err, mp_ord, mp_bool, mp_sign
* MP_USE_ENUMS enables enums
* Wc++-compat catches some implicit conversions if MP_USE_ENUMS is defined
* 100% backwards compatible API/ABI if MP_USE_ENUMS is not defined
win32 rand - just leak the crypt handle
* it will be closed so or so atexit
* the user could request more random data in another atexit routine
leading to another atexit routine being registered