message: build: workaround for FORTIFY_SOURCE=2 builds on Alpine
diff: #ifndef __VIDEOIO_H_
  #define __VIDEOIO_H_
  +#if defined __linux__ || defined __APPLE__ || defined __HAIKU__
  +#include <unistd.h> // -D_FORTIFY_SOURCE=2 workaround: https://github.com/opencv/opencv/issues/15020
  +#endif
  +
  +
  #include "opencv2/videoio.hpp"
  #include "opencv2/videoio/legacy/constants_c.h"
  