Swap --gc-sections to -dead_strip for clang compilation

[jackzhxng]

Description

For release build, since --gc-sections is not supported by clang, use the equivalent, which is -dead_strip (source).

Closes #4874

Test plan

Tested manually:

./.ci/scripts/test_llava.sh Release

[pytorch-bot]

🔗 Helpful Links

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❌ 1 New Failure

As of commit c5c7d5a with merge base 6feb639 ():

NEW FAILURE - The following job has failed:

• trunk / test-llava-runner-macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 137

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[larryliu0820]

Thank you!

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[jackzhxng]

Update: I think dead_strip is for macos, not for clang. Trying if(APPLE) instead.

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