[14] RFR(XS) 8235776: Shenandoah: Shenandoah root updater not always uses right code blob closure

[Roman Kennke]

Ok.

Thanks,
Roman

> Please review this small patch that updates/disarms nmethods during root
> updating if concurrent class unloading is enabled.
> 
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8235776
> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8235776/webrev.00/
> 
> 
> Test:
>   hotspot_gc_shenandoah (fastdebug and release)
> 
> Thanks,
> 
> -Zhengyu
>