I thought atomic_spinlock wasn't too bad, but I like busywait_spinlock.
Of course, I do think it would be better to rename the spinlock itself if it no longer does that....
I guess to facilitate the changeover you could have atomic_lock or busywait_lock (spin is a bit redundant) and mutex, and only very old code would need a typdef for the now non existant 'spinlock' type.