cmd/gc: fix export of inlined function body with type guard

When exporting a body containing
        x, ok := v.(Type)

the definition for Type was not being included, so when the body
was actually used, it would cause an "unknown type" compiler error.

Fixes #4370.

R=ken2
CC=golang-dev
https://golang.org/cl/6827064

src/cmd/gc/export.c

@@ -152,6 +152,7 @@ reexportdep(Node *n)
 	case OCONVIFACE:
 	case OCONVNOP:
 	case ODOTTYPE:
+	case ODOTTYPE2:
 	case OSTRUCTLIT:
 	case OPTRLIT:
 		t = n->type;

test/fixedbugs/issue4370.dir/p1.go

+// Copyright 2012 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 p1
+
+type Magic int
+
+type T struct {
+	x interface{}
+}
+
+func (t *T) M() bool {
+	_, ok := t.x.(Magic)
+	return ok
+}
+
+func F(t *T) {
+	println(t)
+}

test/fixedbugs/issue4370.dir/p2.go

+// Copyright 2012 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 p2
+
+import "./p1"
+
+type T struct {
+	p1.T
+}
+
+func F() {
+	var t T
+	p1.F(&t.T)
+}

test/fixedbugs/issue4370.dir/p3.go

+// Copyright 2012 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 p3
+
+import "./p2"
+
+func F() {
+	p2.F()
+	var t p2.T
+	println(t.T.M())
+}

test/fixedbugs/issue4370.go

+// compiledir
+
+// Copyright 2012 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.
+
+// Re-exporting inlined function bodies missed types in x, ok := v.(Type)
+
+package ignored