Use [[maybe_unused]] instead of DUNE_UNUSED

dune/localfunctions/test/test-finiteelementcache.cc

@@ -21,7 +21,7 @@ static void test(Dune::GeometryType type)
   FiniteElementCache cache;
 
   using FiniteElement = typename FiniteElementCache::FiniteElementType;
-  DUNE_UNUSED const FiniteElement& finiteElement = cache.get(type);
+  [[maybe_unused]] const FiniteElement& finiteElement = cache.get(type);
 }
 
 int main() {

dune/localfunctions/test/virtualshapefunctiontest.cc

@@ -55,7 +55,7 @@ void testLocalBasis(const LocalBasisVirtualInterface<T>* localBasis)
 {
   // call each method once to test that it's there
   syntax_check<unsigned int>( localBasis->order() );
-  unsigned int size DUNE_UNUSED = localBasis->size();
+  [[maybe_unused]] unsigned int size = localBasis->size();
 
   // evaluate the local basis at (0,...,0)
   typename T::DomainType in(0);