Function gmp_mpfr_sys::gmp::__gmpn_add

pub unsafe extern fn __gmpn_add(__gmp_wp: mp_ptr,
                                __gmp_xp: mp_srcptr,
                                __gmp_xsize: mp_size_t,
                                __gmp_yp: mp_srcptr,
                                __gmp_ysize: mp_size_t)
                                -> mp_limb_t