Merge branch 'fix/virtual-destructors' into 'master'

added missing destructors to abstract classes that clang 6 complains about

See merge request nektar/nektar!932

CHANGELOG.md

@@ -49,6 +49,7 @@ v5.0.0
 - Removed instance count from beginning of Array storage to improve memory
   alignment (!921)
 - Fix naming issue of duplicate Unit tests (!924) 
+- Fix warnings about missing virtual destructors in abstract classes (!932)
 
 **NekMesh**:
 - Add feature to read basic 2D geo files as CAD (!731)

library/SolverUtils/Advection/Advection.h

@@ -69,6 +69,10 @@ typedef std::function<void (
 class Advection
 {
 public:
+
+    SOLVER_UTILS_EXPORT virtual ~Advection()
+    {};
+
     /// Interface function to initialise the advection object.
     SOLVER_UTILS_EXPORT void InitObject(
         LibUtilities::SessionReaderSharedPtr               pSession,

library/SolverUtils/Diffusion/Diffusion.h

@@ -71,6 +71,10 @@ namespace Nektar
         class Diffusion
         {
         public:
+
+            SOLVER_UTILS_EXPORT virtual ~Diffusion()
+            {};
+
             SOLVER_UTILS_EXPORT void InitObject(
                 LibUtilities::SessionReaderSharedPtr              pSession,
                 Array<OneD, MultiRegions::ExpListSharedPtr>       pFields);

library/SolverUtils/RiemannSolvers/RiemannSolver.h

@@ -160,6 +160,9 @@ namespace Nektar
             SOLVER_UTILS_EXPORT RiemannSolver(
                 const LibUtilities::SessionReaderSharedPtr& pSession);
 
+            SOLVER_UTILS_EXPORT virtual ~RiemannSolver()
+            {};
+
             virtual void v_Solve(
                 const int                                         nDim,
                 const Array<OneD, const Array<OneD, NekDouble> > &Fwd,