cmd/yacc: fix copying action code when line comment is disabled

Fixes #12601.

Change-Id: I0be69ffe9ba19934aaef1651845c725708db77de
Reviewed-on: https://go-review.googlesource.com/14546Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/yacc/yacc.go

@@ -1284,8 +1284,9 @@ func dumpprod(curprod []int, max int) {
 func cpyact(curprod []int, max int) {
 
 	if !lflag {
-		fmt.Fprintf(fcode, "\n\t\t//line %v:%v\n\t\t", infile, lineno)
+		fmt.Fprintf(fcode, "\n\t\t//line %v:%v", infile, lineno)
 	}
+	fmt.Fprint(fcode, "\n\t\t")
 
 	lno := lineno
 	brac := 0