RFR(T): 8214206: Fix for JDK-8213419 is broken on 32-bit

[Roland Westrelin]

Hi Martin,

> webrev.02 seems to work. But I still wonder why we should have a version which only casts to unsigned.

Thanks for giving it a try. Not sure if a signed + an unsigned versions
are needed. But not relying on implicit casting seems safer.

webrev.02 passes the submit repo. So unless someone objects I'll push it
later today (with a fix for the misleading comment that David pointed
out).

Roland.