[caffe2] fixes to allow stricter compilation flag (#64016)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64016
In order to increase the strictness of the compilation for some target depending on caffe2 we need to fix some errors uncovered when rising such flags.
This change introduces the required override tokens for virtual destructors
Test Plan: CI. Moreover targets depending on caffe2 using clang strict warnings now compile
Reviewed By: kalman5
Differential Revision: D30541714
fbshipit-source-id: 564af31b4a9df3536d7d6f43ad29e1d0c7040551
