Build xnn_executor_runner with cmake (#153)

Summary:
So that the binary can be used in the same way as buck2

Pull Request resolved: https://github.com/pytorch/executorch/pull/153

Reviewed By: kirklandsign

Differential Revision: D48727218

Pulled By: huydhn

fbshipit-source-id: a06c3316e4b6c4c8edbbd309115a2b7283bf8359