[Hardware][Apple] Allows VLLM_TARGET_DEVICE=empty on MacOs

[wallashss]

This small patch allows to users have an "empty install" on mac os if they wish so.

Currently, any install on mac os force to CPU.

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[joerunde]

Can confirm this does allow me to install vLLM on my mac while setting VLLM_TARGET_DEVICE=empty

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This pull request has been automatically marked as stale because it has not had any activity within 90 days. It will be automatically closed if no further activity occurs within 30 days. Leave a comment if you feel this pull request should remain open. Thank you!

[github-actions]

This pull request has been automatically closed due to inactivity. Please feel free to reopen if you intend to continue working on it. Thank you!