Merge commit 'a88e21f5b78ef5e75b073ecbfd4e92921002a703'

* commit 'a88e21f5b78ef5e75b073ecbfd4e92921002a703':
  Fix missing symbols when libvpx has only vp8 enabled

Not merged, the FFmpeg libvpx-vp8 encoder does not use anything from libvpx.c

Merged-by: Michael Niedermayer <michaelni@gmx.at>