message: overdraw: Replace cluster copy loop with memcpy
  This slightly improves performance, 1000 ms -> 980 ms on the test mesh
  set, and simplifies the code.
diff: @@ -325,12 +325,8 @@ void meshopt_optimizeOverdraw(unsigned int* destination, const unsigned int* ind
  size_t end = (cluster + 1 < cluster_count) ? clusters[cluster + 1] : index_count / 3;
  assert(start < end);
  - for (size_t i = start; i < end; ++i)
  - {
  - destination[offset++] = indices[3 * i + 0];
  - destination[offset++] = indices[3 * i + 1];
  - destination[offset++] = indices[3 * i + 2];
  - }
  + memcpy(destination + offset, indices + start * 3, (end - start) * 3 * sizeof(unsigned int));
  + offset += (end - start) * 3;
  }
  assert(offset == index_count);
  