Most ranged weapons will be worse than useless, the only thing that will be even moderately effective are RPG's AKA rocket propelled grenades, even normal grenades will be decently effective. they will fragment the skeleton. But they will really only be useful for getting away or for softening them up as a direct attack method they will leave the skeletons in relatively large pieces. 

If you don't mind going old school, cannon and chain shot will also be somewhat effective. they will rip through a skeleton as if it was not there, with some creativity it might be possible to create a modern equivalent. 

[![enter image description here][1]][1]

A skid steer driven mulching mower, this will not only cut the skeletons apart but you can run it back over the pile to reduce them to nothing but bone chips. The open front combined with the crash bar means you can basically just run into the skeletons. The windows are designed to withstand flying rocks and branches a bow and arrow will not penetrate. A skidsteer is also a lot more fuel efficient than a tank, althou chasly's tank is also a good idea. 

[![enter image description here][2]][2]


For close combat platemail plus a finned mace is your best bet, Once bone is removed from it protective covering of tendon and muscle it is relatively easy to smash. Honestly a baseball bat will work just as well. A pole hammer may be a nice choice as well, although you need a decent amount of room to get the best use out of it. 

[![enter image description here][3]][3]

Bolos and tripwires, will be good for knocking down the skeletons to make them easier to attack. 

Now if you want to get creative, your summoner could summon a Independent Tactical Thagomizer otherwise know a stegosaurus, which will be a able to smash skeletons quite effectively, they are very agile so they can strike a large area, and they are well armored even if they don't look like it. The are covered in armor, skeletons will have a hard time injuring them. An ankylosaur will also work. 
 
[![enter image description here][4]][4]

Of course if you want effective and fun, you can use go the monster truck route, the fuel efficiency is about the same as  tank but one person can drive it, and many run off alcohol so they may even be able to get local fuel. Plus you get to have your character giggling like a lunatics while tearing around the army crushing skeletons under giant tires.  


  [1]: https://i.sstatic.net/m0V4t.jpg
  [2]: https://i.sstatic.net/HVDGU.jpg
  [3]: https://i.sstatic.net/81TfV.jpg
  [4]: https://i.sstatic.net/MOifF.jpg