[release-branch.go1.4] cmd/gc: don't recurse infinitely when a recursive type references itself more than once
Fixes #9432
Change-Id: I08c92481afa7c7fac890aa780efc1cb2fabad528
Reviewed-on: https://go-review.googlesource.com/2115
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Russ Cox <rsc@golang.org>
(cherry picked from commit
fcff3ba740ed6638cece4dea8478bd1dfb2411bf)
Reviewed-on: https://go-review.googlesource.com/5004
Run-TryBot: Andrew Gerrand <adg@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>