fix erfc() usage in cider

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

src/ciderlib/oned/onedopng.c

@@ -90,7 +90,7 @@ ONEdopingValue(DOPprofile *pProfile, DOPtable *pTable, double x)
     if (argP > 10.0) {
       value = 0.0;
     } else {
-      value = pProfile->PEAK_CONC * erfc(-argP);
+      value = pProfile->PEAK_CONC * erfc(argP);
     }
     break;
   case LOOKUP:

src/ciderlib/twod/twodopng.c

@@ -111,7 +111,7 @@ TWOdopingValue(DOPprofile *pProfile, DOPtable *pTable, double x,
     if ( argP > 10.0 ) {
       value = 0.0;
     } else {
-      value = pProfile->PEAK_CONC * erfc( -argP );
+      value = pProfile->PEAK_CONC * erfc( argP );
     }
     break;
   case LOOKUP:
@@ -156,7 +156,7 @@ TWOdopingValue(DOPprofile *pProfile, DOPtable *pTable, double x,
       if ( argP > 10.0 ) {
 	value = 0.0;
       } else {
-	value *= erfc( -argL );
+	value *= erfc( argL );
       }
       break;
     case LOOKUP: