Mac OSS CI use cmake built gtest (#3713)

Summary:
Instead of using buck. Note that for sccache shims, we need to create the tempdir outside of setup-macos.sh, to prevent from files removed after the script finishes.

Pull Request resolved: https://github.com/pytorch/executorch/pull/3713

Reviewed By: huydhn

Differential Revision: D57754547

Pulled By: kirklandsign

fbshipit-source-id: b348c6226ca090e38a07c8f58570ab5539a817ce