cmd/compiler/internal/gc: make Type.Copyto a []*Node

Passes go build -a -toolexec 'toolstash -cmp' std cmd

Change-Id: Ief4613cfb341172a85e3a894f44fb2bb308c7b55
Reviewed-on: https://go-review.googlesource.com/14554
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/compile/internal/gc/go.go

@@ -210,7 +210,7 @@ type Type struct {
 	Embedlineno int32 // first use of TFORW as embedded type
 
 	// for TFORW, where to copy the eventual value to
-	Copyto *NodeList
+	Copyto []*Node
 
 	Lastfn *Node // for usefield
 }

src/cmd/compile/internal/gc/typecheck.go

@@ -3544,7 +3544,7 @@ var mapqueue *NodeList
 func copytype(n *Node, t *Type) {
 	if t.Etype == TFORW {
 		// This type isn't computed yet; when it is, update n.
-		t.Copyto = list(t.Copyto, n)
+		t.Copyto = append(t.Copyto, n)
 
 		return
 	}
@@ -3569,8 +3569,8 @@ func copytype(n *Node, t *Type) {
 	t.Copyto = nil
 
 	// Update nodes waiting on this type.
-	for ; l != nil; l = l.Next {
-		copytype(l.N, t)
+	for _, n := range l {
+		copytype(n, t)
 	}
 
 	// Double-check use of type as embedded type.