cmd/cgo: fix recursive type mapping

Instead of immediately completing pointer type mappings, add them to
a queue to allow them to be completed later.  This fixes issues	caused
by Type() returning arbitrary in-progress type mappings.

Fixes #8368.
Fixes #8441.

LGTM=iant
R=golang-codereviews, iant
CC=golang-codereviews
https://golang.org/cl/122850043
diff --git a/misc/cgo/test/issue8441.go b/misc/cgo/test/issue8441.go
new file mode 100644
index 0000000..2d871f0
--- /dev/null
+++ b/misc/cgo/test/issue8441.go
@@ -0,0 +1,27 @@
+// Copyright 2014 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 8368 and 8441.  Recursive struct definitions didn't work.
+// No runtime test; just make sure it compiles.
+
+package cgotest
+
+/*
+typedef struct one one;
+typedef struct two two;
+struct one {
+	two *x;
+};
+struct two {
+	one *x;
+};
+*/
+import "C"
+
+func issue8368(one *C.struct_one, two *C.struct_two) {
+}
+
+func issue8441(one *C.one, two *C.two) {
+	issue8441(two.x, one.x)
+}