Added missing __cuda_callable__ mark to the Constant function

src/TNL/Functions/Analytic/Constant.h

@@ -27,6 +27,7 @@ class Constant : public Domain< dimensions, NonspaceDomain >
       typedef Real RealType;
       typedef Containers::StaticVector< dimensions, RealType > PointType;
  
+      __cuda_callable__
       Constant();
 
       static void configSetup( Config::ConfigDescription& config,

src/TNL/Functions/Analytic/Constant_impl.h

@@ -16,6 +16,7 @@ namespace Analytic {
 
 template< int Dimension,
           typename Real >
+__cuda_callable__
 Constant< Dimension, Real >::
 Constant()
 : constant( 0.0 )