libvpx

cpplint issues vp9_thread.h

apparently we are going to have trouble completely removing lint issue in this file.
It needs a bit more work.   We need to include vpx_config.h to know whether
we need to have multi threading .    and that means vpx_config.h has to come
before the system headers.  ( a violation )

Change-Id: I023feeab1bf5643b79dccc3b80a4a9ad42689e7b
Signed-off-by: Jim Bankoski <jimbankoski@google.com>