#1209 Replace clang::fallthrough by the newly supported C++ 17 attribute fallthrough.

Sources/Operators/LocalVariationalOperator/CauchyAndInvariant/InvariantHolder.hxx

@@ -72,14 +72,14 @@ namespace MoReFEM
                 {
                     invariants_second_derivative_[i].Resize(size, size);
                 }
-                [[clang::fallthrough]];
+                [[fallthrough]];
             case InvariantHolderNS::Content::invariants_and_first_deriv:
                 static_assert(std::tuple_size<decltype(invariants_first_derivative_)>::value == NinvariantsT);
                 for (unsigned int i = 0u; i < NinvariantsT ; ++i)
                 {
                     invariants_first_derivative_[i].Resize(size);
                 }
-                [[clang::fallthrough]];
+                [[fallthrough]];
             case InvariantHolderNS::Content::invariants:
                 break;
         }
@@ -162,7 +162,7 @@ namespace MoReFEM
                                                                       invariants_second_derivative[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_second_derivative_index::d2I2dCdC)]);
                     SecondDerivativeInvariant3CauchyGreen<DimensionT>(cauchy_green_tensor,
                                                                       invariants_second_derivative[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_second_derivative_index::d2I3dCdC)]);
-                    [[clang::fallthrough]];
+                    [[fallthrough]];
                 case Content::invariants_and_first_deriv:
                     FirstDerivativeInvariant1CauchyGreen<DimensionT>(cauchy_green_tensor,
                                                                      invariants_first_derivative[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_first_derivative_index::dI1dC)]);
@@ -179,7 +179,7 @@ namespace MoReFEM
                                                                          tau_interpolate_at_quad_point,
                                                                          invariants_first_derivative[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_first_derivative_index::dI4dC)]);
                     }
-                    [[clang::fallthrough]];
+                    [[fallthrough]];
                 case Content::invariants:
                     invariants[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_index::I1)] = Invariant1<DimensionT>(cauchy_green_tensor);
                     invariants[EnumUnderlyingType(InvariantHolder<NinvariantsT>::invariants_index::I2)] = Invariant2<DimensionT>(cauchy_green_tensor);