Fix OSS build + separate test build into its own CMakeLists.txt (#3724)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3724

## Context

As title. In the next diff, the vulkan test binary will be added to CI.

imported-using-ghimport

Test Plan: Imported from OSS

Reviewed By: kirklandsign

Differential Revision: D57747739

Pulled By: SS-JIA

fbshipit-source-id: 0829abb08849d5349751c63d2c0c5a5dc39ca553