cmake HAVE_VFW examples

plumonito/dtslam 3rdparty/opencv-git/cmake/OpenCVFindLibsVideo.cmake :7

try_compile(HAVE_VFW
    "${OpenCV_BINARY_DIR}"
    "${OpenCV_SOURCE_DIR}/cmake/checks/vfwtest.cpp"
    CMAKE_FLAGS "-DLINK_LIBRARIES:STRING=vfw32")