Update ffmpeg 2.1.3 -> 5.0.1

Old ffmpeg has a lot of vulnerabilities that have been fixed in newer
versions, see https://www.cvedetails.com/vulnerability-list/vendor_id-3611/Ffmpeg.html.

extern/ffmpeg/libavcodec/cbrt_data.c

@@ -0,0 +1,30 @@
+/*
+ * Copyright (c) 2016 Reimar Döffinger <[email protected]>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "config.h"
+#include "cbrt_data.h"
+
+#include "libavutil/libm.h"
+
+#if CONFIG_HARDCODED_TABLES
+#include "libavcodec/cbrt_tables.h"
+#else
+#include "cbrt_tablegen.h"
+#endif