[PATCH] Replaces __sync_swap with std::atomic

The commented out regions mentioning this worked as is.

I don't know if these were left commented out because they don't work on
some platforms, but they work on OS X. Were they left commented out because
they had been forgotten?

- Dan

Howard, it looks like you’re the one that added the commented out behavior, and your commit said that you “could not yet do that”. Any update?

  • Dan

Howard has moved on to other projects, and I don’t think that email works anymore. Marshall is the current libc++ maintainer, maybe he knows?