RFR: Fix Shenandoah non-PCH build

[Aleksey Shipilev]

On 08/20/2018 02:57 PM, Zhengyu Gu wrote:
> Non-PCH build broke again.
> 
> http://cr.openjdk.java.net/~zgu/shenandoah/sh-non-pch/webrev.00/index.html

Looks good.

That's it? I thought we get more failures without this one:
  https://bugs.openjdk.java.net/browse/JDK-8209647

-Aleksey