This is a reminder issue to add some test cases of uses of imported constraint types in a pre-1.18 package.
We already have a test file (cmd/compile/internal/types2/testdata/fixedbugs/issue47818.go2) that just needs to be extended.

We should do this once we have a constraints package checked in; then we can just import that package. (Right now the test harness for types2 doesn't easily allow this.)

For instance, once #45458 is implemented, this issued could be addressed trivially.