cmd/compile: reject anonymous interface cycles

This CL changes cmd/compile to reject anonymous interface cycles like:

	type I interface { m() interface { I } }

We don't anticipate any users to be affected by this change in
practice. Nonetheless, this CL also adds a `-d=interfacecycles`
compiler flag to suppress the error. And assuming no issue reports
from users, we'll move the check into go/types and types2 instead.

Updates #56103.

Change-Id: I1f1dce2d7aa19fb388312cc020e99cc354afddcb
Reviewed-on: https://go-review.googlesource.com/c/go/+/445598
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Matthew Dempsky <mdempsky@google.com>

test/fixedbugs/issue56103.go

@@ -0,0 +1,46 @@
+// errorcheck
+
+// Copyright 2022 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.
+
+package p
+
+// Self recursion.
+type i interface{ m() interface{ i } } // ERROR "invalid recursive type"
+type _ interface{ i }                  // no redundant error
+
+// Mutual recursion.
+type j interface{ m() interface{ k } } // ERROR "invalid recursive type"
+type k interface{ m() interface{ j } }
+
+// Both self and mutual recursion.
+type (
+	a interface { // ERROR "invalid recursive type"
+		m() interface {
+			a
+			b
+		}
+	}
+	b interface {
+		m() interface {
+			a
+			b
+		}
+	}
+)
+
+// Self recursion through other types.
+func _() { type i interface{ m() *interface{ i } } }        // ERROR "invalid recursive type"
+func _() { type i interface{ m() []interface{ i } } }       // ERROR "invalid recursive type"
+func _() { type i interface{ m() [0]interface{ i } } }      // ERROR "invalid recursive type"
+func _() { type i interface{ m() chan interface{ i } } }    // ERROR "invalid recursive type"
+func _() { type i interface{ m() map[interface{ i }]int } } // ERROR "invalid recursive type"
+func _() { type i interface{ m() map[int]interface{ i } } } // ERROR "invalid recursive type"
+func _() { type i interface{ m() func(interface{ i }) } }   // ERROR "invalid recursive type"
+func _() { type i interface{ m() func() interface{ i } } }  // ERROR "invalid recursive type"
+func _() {
+	type i interface { // ERROR "invalid recursive type"
+		m() struct{ i interface{ i } }
+	}
+}