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

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

Change-Id: I06d944aaa168fb595ff96eb27a7d6e7da344ebd6
Reviewed-on: https://go-review.googlesource.com/118564
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Andrew Bonventre <andybons@golang.org>

go/internal/gccgoimporter/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 gccgoimporter
+
+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/gccgoimporter/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 gccgoimporter
+
+import "go/types"
+
+func newInterface(methods []*types.Func, embeddeds []types.Type) *types.Interface {
+	return types.NewInterface2(methods, embeddeds)
+}

go/internal/gccgoimporter/parser.go

@@ -602,7 +602,7 @@ func (p *parser) parseInterfaceType(pkg *types.Package) types.Type {
 	}
 	p.expect('}')
 
-	return types.NewInterface2(methods, embeddeds)
+	return newInterface(methods, embeddeds)
 }
 
 // PointerType = "*" ("any" | Type) .