Combining revisions with only-arch allows specifying
that a test only applies to a handful of targets.
This allows removing a large amount of repetition
in the test suite for tests that do not benefit.
The revisions are suboptimal for this for some tests,
so they aren't preferred in those cases.
The was careful around not calling `fn_sig` on not-functions but well,
it wasn't careful enough. This commit makes it a little more careful and
also adds tests for a bunch more item kinds.
