[compiler-rt] [Apple][RTSan] Realtime sanitizers are failing in Apple CI (PR #124873)

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thetruestblue wrote:

> Would you elaborate on what was going wrong for future info? I'm curious!

To @jroelofs point I just skipped these internally for now. I think the OSSpinLock behavior is likely explained by how you're forward declaring the symbol, and how there are situations where we are replacing these with a macro, our TSan tests started failing in the same way recently (I pointed you to the TSan fix). I don't have a good explanation for the ___atomic_is_lock_free not being available at this point (though in one of our jobs this fails without that error). I'm going to schedule some time to look into this, and I'll put up a PR when I have a chance to actually investigate. 

https://github.com/llvm/llvm-project/pull/124873