cmd/compile: slightly more idiomatic println code

Updates #21808.

Change-Id: I0314426afcfeed17b1111040110d7f2b0e209526
Reviewed-on: https://go-review.googlesource.com/62430
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -2071,10 +2071,10 @@ func walkprint(nn *Node, init *Nodes) *Node {
 		s := nn.List.Slice()
 		t := make([]*Node, 0, len(s)*2)
 		for i, n := range s {
-			t = append(t, n)
-			if i != len(s)-1 {
+			if i != 0 {
 				t = append(t, nodstr(" "))
 			}
+			t = append(t, n)
 		}
 		t = append(t, nodstr("\n"))
 		nn.List.Set(t)