[dev.cc] cmd/internal/obj, cmd/new9a: use ctxt.NewProg

cmd/internal/obj reconverted using rsc.io/c2go rev 40275b8.

All Prog*s need Ctxt field set so that the printer can tell
which architecture the Prog belongs to.
Use ctxt.NewProg consistently for this.

Change-Id: Ic981b3d68f24931ffae74a772e83a3dc2fdf518a
Reviewed-on: https://go-review.googlesource.com/3152
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/obj/link.go

@@ -49,7 +49,7 @@ type Addr struct {
 	Class   int8
 	Etype   uint8
 	Offset2 int32
-	Node    *struct{}
+	Node    interface{}
 	Width   int64
 }