[!794] [hybrid] Make evaluateFoldExpression constexpr to enable use in constexpr functions

Merge branch 'fix/hybridutility-constexpr' into 'master'

See merge request [core/dune-common!794]

  [core/dune-common!794]: Nonecore/dune-common/merge_requests/794

dune/common/hybridutilities.hh

@@ -209,7 +209,7 @@ constexpr auto integralRange(const End& end)
 namespace Impl {
 
   template<class T>
-  void evaluateFoldExpression(std::initializer_list<T>&&)
+  constexpr void evaluateFoldExpression(std::initializer_list<T>&&)
   {}
 
   template<class Range, class F, class Index, Index... i>