Discussion of issue 22980 made it clear to me that part of the problem with the cross-build support is that the difference between the build time information exposed in sysconfig and the live system information exposed in the platform module isn't clear.

Debian's multiarch triplets (https://wiki.debian.org/Multiarch/Tuples) describe this information well, but it currently isn't readily exposed to Python code. sysconfig.get_config_var("MULTIARCH") only works on Debian & derivatives, and even issue 22980 only exposes the information in sysconfig.get_config_var("SOABI") on a subset of platforms.

It would be good to extend the triples to cover Windows, and also to expose the *current* system triple at runtime in the platform module (including appropriate normalisation)