Switch to 9.0 prerelease branch
    
    - Today's git snap of same
    - Switch to irritatingly-slow swrast instead of intolerably-slow softpipe
      on non-llvm arches
    - Re-disable llvm on PPC until it's in shape enough to make pixels appear
    - Drop libGLU subpackage, split off upstream
    - Drop manpages, require gl-manpages from libGL-devel instead
    - Capitulate to libkms until upstream stops needing it again