cider relied on our broken ngspice variant of erfc() which behaved as
erfc_ngspice(x) = erfc(fabs(x))
Note:
apart from cider, erfc is used in
devices/ltra/ltramisc.c
always with positive argument
and
src/frontend/spec.c
again always with positive argument
Thus, the difference in implementation
never mathered anywhere except in cider