use if constexpr to eliminate some foam code

opm/simulators/wells/MultisegmentWell_impl.hpp

@@ -73,7 +73,7 @@ namespace Opm
             OPM_THROW(std::runtime_error, "energy is not supported by multisegment well yet");
         }
 
-        if (Base::has_foam) {
+        if constexpr (Base::has_foam) {
             OPM_THROW(std::runtime_error, "foam is not supported by multisegment well yet");
         }
 

opm/simulators/wells/StandardWell_impl.hpp

@@ -793,7 +793,7 @@ namespace Opm
             }
         }
 
-        if (has_foam) {
+        if constexpr (has_foam) {
             // TODO: the application of well efficiency factor has not been tested with an example yet
             const unsigned gasCompIdx = Indices::canonicalToActiveComponentIndex(FluidSystem::gasCompIdx);
             EvalWell cq_s_foam = cq_s[gasCompIdx] * well_efficiency_factor_;