webrev for hsail support for CompareAndSwap and Membar

[Deneau, Tom]

I have posted a webrev enabling HSAIL backend support for CompareAndSwapNode to http://cr.openjdk.java.net/~tdeneau/graal-webrevs/webrev-compareandswap/webrev/ 

This  webrev also adds support for a volatile load and store with emitMembar.  

I added the CompareAndSwap support to  HSAILHotSpotLIRGenerator (instead of HSAILLIRGenerator) because of the hotspot-specific special handling when the CAS location is a compressed oop. (This was definitely the more complicated case to implement).

Three test cases were also added, using each of AtomicInteger, AtomicLong and AtomicReference.

Could you please look this over?

-- Tom