gc: fix method offsets of anonymous interfaces

Fixes #1290.

R=rsc
CC=golang-dev
https://golang.org/cl/3259043

src/cmd/gc/dcl.c

@@ -844,6 +844,8 @@ dostruct(NodeList *l, int et)
 		t->broke = 1;
 		return t;
 	}
+	if(et == TINTER)
+		t = sortinter(t);
 	if(!funarg)
 		checkwidth(t);
 	return t;

src/cmd/gc/go.y

@@ -1726,7 +1726,6 @@ hidden_type_misc:
 |	LINTERFACE '{' ohidden_interfacedcl_list '}'
 	{
 		$$ = dostruct($3, TINTER);
-		$$ = sortinter($$);
 	}
 |	'*' hidden_type
 	{

src/cmd/gc/typecheck.c

@@ -263,7 +263,6 @@ reswitch:
 		n->type = dostruct(n->list, TINTER);
 		if(n->type == T)
 			goto error;
-		n->type = sortinter(n->type);
 		break;
 
 	case OTFUNC:

test/fixedbugs/bug314.go

+// $G $D/$F.go && $L $F.$A && ./$A.out || echo BUG: bug314
+
+// Copyright 2010 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.
+
+// Used to call wrong methods; issue 1290.
+
+package main
+
+type S struct {
+}
+func (S) a() int{
+	return 0
+}
+func (S) b() int{
+	return 1
+}
+
+func main() {
+	var i interface {
+		b() int
+		a() int
+	} = S{}
+	if i.a() != 0 {
+		panic("wrong method called")
+	}
+	if i.b() != 1 {
+		panic("wrong method called")
+	}
+}