webrev: use assumeTrue to check for simulator

[Caspole, Eric]

Hi everybody,
I put a new webrev here:

http://cr.openjdk.java.net/~ecaspole/reduce_no_sim/webrev/

The reduce tests already checked in only work when built using the Sumatra JDK and -Dcom.amd.sumatra.offload.immediate=true is used. The HSAIL Simulator does not support HSA group/local memory at this time, so if you run the tests with the JDK and the flag under the simulator, they will fail. Here I added "assumeTrue" to skip the test if running on the simulator which makes it easier for me to work with and test the Sumatra JDK.
This change will have no effect when you build Graal using plain JDK 8 since it will not offload the reduce operations.
Regards,
Eric