SumOp for int32 (#23995)
Summary:
as title, the op can be used to update Length blob values in cuda.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23995
Reviewed By: xianjiec
Differential Revision: D16684065
fbshipit-source-id: da562334c8b61a5e54c3aa78156ce5caff619e60
