Somebody has already found a way to compile C++ code for the cRIO with gcc
here.
However, unless you are very familiar with this sort of thing, I'd recommend not using it. The problem is that if something goes wrong, and you don't know what it is, only a few people on Chief Delphi can help you. If it doesn't work while you're at competition, none of the FTA's can fix it for you. Using the gcc toolchain will take longer, and it will take a while to get used to. You'll need a computer that runs windows to image the cRIO and drive the robot, so why don't you put windriver on that?