RFR [9] 8140606: Update library code to use internal Unsafe

[Chris Hegarty]

Following on from 8139891 "Prepare Unsafe for true encapsulation” [1],
the JDK library code should use the internal Unsafe class, and not
sun.misc.Unsafe.

http://cr.openjdk.java.net/~chegar/8140606/00/

This will be pushed to jdk9/dev once 8139891 makes its way from
hs-rt.

-Chris.

[1] https://bugs.openjdk.java.net/browse/JDK-8139891