Um, there's https://github.com/Homebrew/formula-patches/pull/95...As mentioned in https://github.com/Homebrew/homebrew-core/pull/7421#issuecomment-266127277, build and test would have succeeded even if `clock_gettime` were linked on 10.11 :)
However, since I'm intimately familiar with this patch and have done local testing, it should be fine.