[12] RFR(XS): 8210164: building Minimal VM fails with error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]

[Aleksei Voitylov]

Hi,

please review this patch which fixes Minimal VM build error after 
b9f6a4427da9 was pushed. I'm suggesting to fix it explicitly as opposed 
to disabling the compiler warning.

bug: https://bugs.openjdk.java.net/browse/JDK-8210164
webrev: http://cr.openjdk.java.net/~avoitylov/webrev.8210164.02/

Tested by running hotspot regression tests.

Thanks,

-Aleksei