[JDK10] RFR: Silence compilation warnings on implicit type conversion

[Zhengyu Gu]

Finally, built Shenandoah JDK10 with VS 2013 update 3.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/silence_win_warnings-jdk10/webrev.00/

Test:

   Built on Windows


Thanks,

-Zhengyu