Static assertion that AtomicWord is integral is backwards. In this code:

MONGO_STATIC_ASSERT(!std::is_integral<T>::value ||                         
        sizeof(T) == sizeof(atomic_word_detail::Base<T>));

should be `std::is_integral<T>::value`. Fortunately everything still compiles with that fix, at least on Intel.

However, instead I'm removing this assertion all together and replacing with TODO from a while back to implement `std::atomic<WordType>::is_always_lock_free` assertion.