x11-toolkits/nucleo: unbreak with ffmpeg 4.0

ffmpegImageSink.cxx:137:39: error: use of undeclared identifier 'AVFMT_RAWPICTURE'

} else if (output_format->flags & AVFMT_RAWPICTURE) {
                                  ^

ffmpegImageSink.cxx:198:20: error: no member named 'me_method' in 'AVCodecContext'

codec_context->me_method = ME_EPZS ; // ME_ZERO
~~~~~~~~~~~~~  ^

ffmpegImageSink.cxx:198:32: error: use of undeclared identifier 'ME_EPZS'

codec_context->me_method = ME_EPZS ; // ME_ZERO
                           ^

ffmpegImageSink.cxx:212:27: error: use of undeclared identifier 'CODEC_FLAG_GLOBAL_HEADER'

codec_context->flags |= CODEC_FLAG_GLOBAL_HEADER ;
                        ^

PR: 227726
Reported by: antoine (via exp-run)