message: simplify: Fix Travis build
  CoarseCell structure must have external linkage for it to be useful
  inside allocate<> template function.
diff: @@ -905,6 +905,19 @@ struct TriangleHasher
  }
  };
  +struct CoarseCell
  +{
  + union {
  + float error;
  + unsigned int errorui;
  + };
  + unsigned int degenerate_triangles;
  + unsigned int best_vertex;
  + // TODO: it simplifies the algorithm to have this, but it's a lot of memory; can we do better?
  + unsigned int fine_cells[8];
  + unsigned int fine_cell_count;
  +};
  +
  } // namespace meshopt
  #if TRACE
  @@ -1409,19 +1422,6 @@ size_t meshopt_simplifySloppy(unsigned int* destination, const unsigned int* ind
  }
  // let's create an array of coarse cells
  - struct CoarseCell
  - {
  - union {
  - float error;
  - unsigned int errorui;
  - };
  - unsigned int degenerate_triangles;
  - unsigned int best_vertex;
  - // TODO: it simplifies the algorithm to have this, but it's a lot of memory; can we do better?
  - unsigned int fine_cells[8];
  - unsigned int fine_cell_count;
  - };
  -
  CoarseCell* coarse_cells = allocator.allocate<CoarseCell>(cell_count);
  size_t coarse_cell_count = 0;
  