webrev for loading HSAIL/Okra function pointers

[Caspole, Eric]

Hi everybody,
Here is a webrev to do null checks on the Okra library we load to do the HSAIL offload. Earlier there were no checks on finding the function pointers, so if you happened to be running an older version of Okra from github, it would crash.

 http://cr.openjdk.java.net/~ecaspole/check_okra_funcs/

Here I made the function pointer loading very similar to the PTX version using macros with null checks.
Thanks,
Eric