Fix TBB compilation on OS X.
Fix TBB compilation on OS X.

The TBB makefile has its own logic for choosing a compiler, and on OS X 10.7 it picks Clang, even though that will fail to build. We use the CXX argument to the SConstruct to override this, giving us a GCC build by default.

GafferHQ/gaffer,cedriclaunay/gaffer,cedriclaunay/gaffer,johnhaddon/gaffer,lucienfostier/gaffer,cedriclaunay/gaffer,appleseedhq/gaffer,hradec/gaffer,lucienfostier/gaffer,cedriclaunay/gaffer,hradec/gaffer,appleseedhq/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,chippey/gaffer,ImageEngine/gaffer,chippey/gaffer,boberfly/gaffer,hradec/gaffer,chippey/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,andrewkaufman/gaffer,boberfly/gaffer,goddardl/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,goddardl/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,boberfly/gaffer,johnhaddon/gaffer,hradec/gaffer,ivanimanishi/gaffer,johnhaddon/gaffer,boberfly/gaffer,GafferHQ/gaffer,goddardl/gaffer,ImageEngine/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,goddardl/gaffer,chippey/gaffer,hradec/gaffer