cmd/compile: use "init... cycle" instead of "init... loop" in error messages

cmd/compile: use "init... cycle" instead of "init... loop" in error messages

For #55326.

Change-Id: Ia3c1124305986dcd49ac769e700055b263cfbd59
Reviewed-on: https://go-review.googlesource.com/c/go/+/432615
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@google.com>