message: Fix rcm declare reduction error
  The omp reduction initializer interacted badly with the wrapper ctor.
diff: @@ -769,7 +769,6 @@ IndexType handle_isolated_nodes(std::shared_ptr<const OmpExecutor> exec,
  // Using a gko::vector here makes clang and gcc segfault,
  // if we then use 'omp_priv = omp_orig'.
  std::vector<IndexType> nodes;
  - IsolatedNodes() : nodes(std::vector<IndexType>(0)) {}
  IsolatedNodes &operator+=(const IsolatedNodes &rhs)
  {
  nodes.reserve(nodes.size() + rhs.nodes.size());
  @@ -778,10 +777,7 @@ IndexType handle_isolated_nodes(std::shared_ptr<const OmpExecutor> exec,
  }
  };
  -#pragma omp declare reduction(FindIsolated \
  - : IsolatedNodes \
  - : omp_out += omp_in) \
  - initializer(omp_priv = IsolatedNodes())
  +#pragma omp declare reduction(FindIsolated : IsolatedNodes : omp_out += omp_in)
  auto isolated = IsolatedNodes();
  #pragma omp parallel for reduction(FindIsolated : isolated)
  for (auto i = 0; i < num_vertices; ++i) {
  