I had a similar problem on ubuntu-20.04 (again, this is the update which introduced gmp-6.2); I had to remove the lines
Code:
#if GMP_LIMB_BITS == 64
dest->_mp_d[0] = src;
dest->_mp_size = (src ? 1 : 0);
#else
from include/gmp_xface.h to get something which worked, it sounds as if the internal representation of gmp objects may have changed