[dev.ssa] test: fix build

Add line that was inadvertently removed.

Change-Id: I99ebc1041e984e408ae5825836c28b9891d6043b
Reviewed-on: https://go-review.googlesource.com/14470
Run-TryBot: Todd Neal <todd@tneal.org>
Reviewed-by: Keith Randall <khr@golang.org>

test/run.go

@@ -636,6 +636,7 @@ func (t *test) run() {
 		}
 
 	case "run":
+		useTmp = false
 		ssaMain = true
 		out, err := runcmd(append([]string{"go", "run", t.goFileName()}, args...)...)
 		if err != nil {