fix xnn executor runner cmake (#2613)

Summary:
the xnnpack backend's cmake refactor lost the portable_ops_lib for xnn_executor_runner so adding it back in this diff

Pull Request resolved: https://github.com/pytorch/executorch/pull/2613

Reviewed By: guangy10, kirklandsign

Differential Revision: D55277429

Pulled By: mcr229

fbshipit-source-id: c7f4dd5df52df5dc0cfec945ac5da635d7617baa