Instead of intersecting system strings, we filter with the sort of
patterns used in `meta.platforms`.
Indicating this change `forTheseSystems` has been renamed to
`forMatchingSystems`, since the given list is now patterns to match, and
not the systems themselves. [Just as with `meta.platforms`, systems
strings are also supported for backwards compatibility.]
This is more flexible, and makes the `forMatchingSystems` and
packagePlatforms` cases more analogous.
192f4144b2