configure: Disable webm_io when target is VS 7/8/9.
configure: Disable webm_io when target is VS 7/8/9.

libwebm now requires stdint.h, and the noted Visual Studio versions
omit it.

Change-Id: I7e5de131c357cb7a99c33452b2b623882817df0f

Topopiccione/libvpx,Topopiccione/libvpx,mwgoldsmith/vpx,GrokImageCompression/aom,webmproject/libvpx,luctrudeau/aom,Topopiccione/libvpx,Topopiccione/libvpx,webmproject/libvpx,mbebenita/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,mwgoldsmith/vpx,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,GrokImageCompression/aom,smarter/aom,mwgoldsmith/libvpx,mbebenita/aom,mwgoldsmith/vpx,GrokImageCompression/aom,smarter/aom,luctrudeau/aom,Topopiccione/libvpx,mwgoldsmith/vpx,luctrudeau/aom,mwgoldsmith/libvpx,mwgoldsmith/libvpx,webmproject/libvpx,webmproject/libvpx,smarter/aom,mwgoldsmith/libvpx,webmproject/libvpx,smarter/aom,mbebenita/aom,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,smarter/aom,mwgoldsmith/libvpx,luctrudeau/aom,mwgoldsmith/libvpx,Topopiccione/libvpx,ShiftMediaProject/libvpx,smarter/aom,mbebenita/aom,mbebenita/aom,ShiftMediaProject/libvpx,GrokImageCompression/aom,luctrudeau/aom,mwgoldsmith/vpx,GrokImageCompression/aom,webmproject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx