The ADDLmodify/SUBLmodify/ANDLmodify/ORLmodify/XORLmodify should
have clobberFlags set to true.

Change-Id: Ie447d536db51334eddc70c00a722647282186a69
Reviewed-on: https://go-review.googlesource.com/122556
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>