[JDK11] RFR: Silence compilation warnings on implicit type conversion

[Aleksey Shipilev]

On 09/04/2018 07:48 PM, Zhengyu Gu wrote:
> This is Shenandoah JDK11 specific one, others should be fixed vs. Shenandoah JDK backport.

Can you please include those changes into this push as well, and test Windows builds in sh/jdk11 are
fine?

> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/silence_win_warnings_jdk11/webrev.00/

Looks good.

-Aleksey