go/internal/gcimporter: use types.NewInterface (not NewInterface2) for builds before Go 1.11

For https://github.com/golang/lint/issues/402.

Change-Id: If8802c93679af57bcb50c43f386f37458813d910
Reviewed-on: https://go-review.googlesource.com/118563
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

go/internal/gcimporter/bimport.go

@@ -538,7 +538,7 @@ func (p *importer) typ(parent *types.Package, tname *types.Named) types.Type {
 			embeddeds = append(embeddeds, p.typ(parent, nil))
 		}
 
-		t := types.NewInterface2(p.methodList(parent, tname), embeddeds)
+		t := newInterface(p.methodList(parent, tname), embeddeds)
 		p.interfaceList = append(p.interfaceList, t)
 		if p.trackAllTypes {
 			p.typList[n] = t

go/internal/gcimporter/newInterface10.go

@@ -0,0 +1,21 @@
+// Copyright 2018 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.
+
+// +build !go1.11
+
+package gcimporter
+
+import "go/types"
+
+func newInterface(methods []*types.Func, embeddeds []types.Type) *types.Interface {
+	named := make([]*types.Named, len(embeddeds))
+	for i, e := range embeddeds {
+		var ok bool
+		named[i], ok = e.(*types.Named)
+		if !ok {
+			panic("embedding of non-defined interfaces in interfaces is not supported before Go 1.11")
+		}
+	}
+	return types.NewInterface(methods, named)
+}

go/internal/gcimporter/newInterface11.go

@@ -0,0 +1,13 @@
+// Copyright 2018 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.
+
+// +build go1.11
+
+package gcimporter
+
+import "go/types"
+
+func newInterface(methods []*types.Func, embeddeds []types.Type) *types.Interface {
+	return types.NewInterface2(methods, embeddeds)
+}