[Pytorch Delegated Backend] Add macro to define sentinel value of debug handle. (#66584)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66584
This will help avoid "-1"s in different places in our and backend codebase when
debug handle is not known.
Test Plan: CI
Reviewed By: sxu
Differential Revision: D31614478
fbshipit-source-id: 97fceb04e3e78f52feda7b1ba1da08fa4480dd77
