Fix compiler warnings

Author: fwesselm

highs/ipm/IpxWrapper.cpp

@@ -1470,5 +1470,4 @@ HighsStatus reportHipoCrossoverStatus(const HighsOptions& options,
                  "Hipo: Crossover unrecognised status\n");
     return HighsStatus::kError;
   }
-  return HighsStatus::kError;
 }

highs/lp_data/HighsIis.cpp

@@ -272,7 +272,7 @@ bool HighsIis::rowValueBounds(const HighsLp& lp, const HighsOptions& options) {
     }
   }
   bool below_lower = false;
-  bool above_upper;
+  bool above_upper = false;
   for (HighsInt iRow = 0; iRow < lp.num_row_; iRow++) {
     below_lower = upper_value[iRow] <
                   lp.row_lower_[iRow] - options.primal_feasibility_tolerance;

highs/presolve/HighsPostsolveStack.h

@@ -339,6 +339,12 @@ class HighsPostsolveStack {
       case ReductionType::kSlackColSubstitution: {
         return "Slack col substitution";
       }
+      case ReductionType::kImpliedEquation: {
+        return "Implied equation";
+      }
+      case ReductionType::kZeroObjSingletonContinuousCol: {
+        return "Zero obj singleton continuous col";
+      }
       default:
         return "Unknown";
     }