Older LLVM compilers do not support aggregate initialization type deduction

llvm/llvm-project#54050
Implemented llvm/llvm-project@632dd6a
07/2023, first appeared in Clang 17

Author: aprokop

src/spatial/detail/ArborX_IndexableGetter.hpp

@@ -76,15 +76,13 @@ struct Indexables
   KOKKOS_FUNCTION auto size() const { return _values.size(); }
 };
 
-#ifdef KOKKOS_ENABLE_CXX17
 template <typename Values, typename IndexableGetter>
 #if KOKKOS_VERSION >= 40400
 KOKKOS_DEDUCTION_GUIDE
 #else
 KOKKOS_FUNCTION
 #endif
     Indexables(Values, IndexableGetter) -> Indexables<Values, IndexableGetter>;
-#endif
 
 } // namespace Details