project: Fix potentially incompatibility due to double slash in intermediary dir.
project: Fix potentially incompatibility due to double slash in intermediary dir.

mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/vpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,mwgoldsmith/libvpx,mwgoldsmith/libvpx