Based on John's thoughtful comments, a little experimentation and the
multi-arch tuples at <https://wiki.debian.org/Multiarch/Tuples>, SRFI
176 is at a stage where I'm personally happy to call it done. Just need
to update the SRFI document (will take a while; many changes to details
but none to the general approach).

I'm happy to add new properties and discuss any other changes to meet
other people's requirements, and would like to take this opportunity to
remind people that the specification is fully backward-compatible with
every Scheme implementation I could find ;-)

Arthur: I have code to read the version output using grep|sed, awk, C,
Scheme, Common Lisp, Emacs Lisp and Clojure. Should I submit all of it
as the sample implementation?