[dev.ssa] cmd/compile/internal/gc: implement more no-op statements

Change-Id: I26c268f46dcffe39912b8c92ce9abb875310934f
Reviewed-on: https://go-review.googlesource.com/12100Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -294,7 +294,7 @@ func (s *state) stmt(n *Node) {
 	case OBLOCK:
 		s.stmtList(n.List)
 
-	case OEMPTY:
+	case OEMPTY, ODCLCONST, ODCLTYPE:
 
 	case ODCL:
 		if n.Left.Class&PHEAP == 0 {