small webrev to avoid loading the hsail okra library twice

[Deneau, Tom]

I posted a small webrev whose purpose is to avoid loading the hsail okra shared library twice.  It turns out that some features of the hsail simulator okra flavor (in particular, gdb symbols for the simulated HSAIL code and the hsail registers) do not work properly when the library is loaded twice.

I didn't know if there was an os-independent way to check that a library was already loaded, so I wrapped I in #ifdef LINUX.  But for now this logic should only be required on linux anyway.

http://cr.openjdk.java.net/~tdeneau/graal-webrevs/webrev-hsail-avoid-double-dll-load/

-- Tom