RFR: JDK-8141634 Implement VarHandles/Unsafe intrinsics on SPARC

[Trevor Watson]

Hi All,

Please can I get a review of these updates to sparc.ad which adds in the 
C2 compareAndExchange intriniscs for int, long, pointer and object?

I've run the hotspot jtreg tests locally and the JPRT hotspot tests 
successfully.

The implementation of these intrinsics gives a 9x to 20x performance 
improvement for compareAndExchange operatios.

http://cr.openjdk.java.net/~alanbur/JDK-8141634/

Thanks,
Trevor