They are present in R4RS and R5RS, but not IEEE Scheme (which is our baseline). There are problems with a straightforward implementation that SRFI 45 fixes, but we voted down SRFI 45. Given that, we should consider removing them from the standard altogether. (Of course this does not mean compliant implementations can't provide them, it just means they won't be in a standard module.)
We voted tentatively to add the SRFI-45 lazy.