[dev.typealias] cmd/compile: improved error message for cyles involving type aliases

Known issue: #18640 (requires a bit more work, I believe).

For #18130.

Change-Id: I53dc26012070e0c79f63b7c76266732190a83d47
Reviewed-on: https://go-review.googlesource.com/35129


Reviewed-by: Matthew Dempsky <mdempsky@google.com>