Fix missing define statement in previous commit

src/scheme/HyperelasticSolver.cpp

@@ -76,14 +76,18 @@ class HyperelasticSolverHandler::HyperelasticSolver final : public HyperelasticS
   class FixedBoundaryCondition;
   class PressureBoundaryCondition;
   class NormalStressBoundaryCondition;
+#ifdef PUGS_HAS_COSTO
   class CplDirichletBoundaryCondition;
+#endif   // PUGS_HAS_COSTO
   class SymmetryBoundaryCondition;
   class VelocityBoundaryCondition;
 
   using BoundaryCondition = std::variant<FixedBoundaryCondition,
                                          PressureBoundaryCondition,
                                          NormalStressBoundaryCondition,
+#ifdef PUGS_HAS_COSTO
                                          CplDirichletBoundaryCondition,
+#endif   // PUGS_HAS_COSTO
                                          SymmetryBoundaryCondition,
                                          VelocityBoundaryCondition>;