XT is long gone, that was mainly for compatibility with older machines that were still around a few years ago.

I think the detection should centered on the pe though since that's really why there's any cray specific logic and what the whole cray module system is tied to. The only reason to even bother with the cnl/cle version is usually just a sanity check that the craype environment is being used on a cray. In that sense the cle version isn't really needed for anything. Tying "platform=cray" to the pe has the advantage of being able to treat the fronted like normal Linux and directly use the compilers while the pe wrappers are used for compute nodes.

All that is likely a bigger shift though that will need some more thinking through. I agree that a minimal diff to fix the blue waters issue is ideal here and separate from the bigger conversation on how spack sees "cray".

Okay, I left out all of the environment variable checks this time and added unit tests. This should be ready for a final review.