cmd/compile: skip array bounds errors when type is broken

This avoids false positives
like those found in #19880.

Fixes #19880

Change-Id: I583c16cc3c71e7462a72500db9ea2547c468f8c1
Reviewed-on: https://go-review.googlesource.com/40255
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

test/fixedbugs/issue7525c.go

@@ -0,0 +1,13 @@
+// errorcheck
+
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 7525: self-referential array types.
+
+package main
+
+var z struct {
+	e [cap(z.e)]int // ERROR "array bound|typechecking loop|invalid array"
+}