Buildbot: switch to using native toolkit again

Crosscompiling of cubins doesn't work on linux with toolkit 4.2,
so use native toolkit for now. Disabled sm_13 for 32bit platform
for now.

Would keep cudakernels build target for a while. It doesn't hurt
being in the code and it could be helpful again once we'll switch
to toolkit 5.x where crosscompilation works fine.

Some further tweaks could probably be needed still, let's see how
building goes on buildbot now :)

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54465 954f8c5b-7b00-dc11-b283-0030488c597c