message: configure render primitive pool so it works with msvc
  a 64 bytes pool seems to work with both clang and msvc, unfortunately,
  c++ doesn't let us know the allocator object size at compile time
  for map containers, so we have to guess.
diff: @@ -75,18 +75,12 @@ private:
  };
  - // the std::set<T> node size is sizeof(std::set<T>::node_type) + sizeof(T), aligned.
  - // we need this value for our pool allocator. On clang 64 bits this is 56 bytes.
  - using DummySetAllocator = utils::STLAllocator<Entry, utils::Arena<
  - utils::PoolAllocator<8>, utils::LockingPolicy::NoLock>>;
  - using DummySetNode = std::pair<std::set<Entry, std::less<>, DummySetAllocator>::node_type, Entry>;
  -
  // Size of the arena used for the "set" part of the bimap
  static constexpr size_t SET_ARENA_SIZE = 4 * 1024 * 1024;
  // Arena for the set<>, using a pool allocator inside a heap area.
  using Arena = utils::Arena<
  - utils::PoolAllocator<sizeof(DummySetNode)>,
  + utils::PoolAllocator<64>, // this seems to work with clang and msvc
  utils::LockingPolicy::NoLock,
  #ifndef NDEBUG
  utils::TrackingPolicy::HighWatermark,
  