But wait! That’s all theoretical because the bag always has (target #f)
and ‘copy-build’ bundles build and host inputs together, as if doing a
native build.

So it seems like https://issues.guix.gnu.org/70492 (putting everything
in ‘build-inputs’) is OK, after all.

But still, there seem to be some expectation that ‘copy-build-system’
can support cross-compilation for real, so maybe we should add a
‘copy-cross-build’ procedure in addition to the patch above.

Thoughts?

Ludo’.