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/tools/Makefile

@@ -0,0 +1,28 @@
+TOOLS = enum_options qt-faststart scale_slice_test trasher uncoded_frame
+TOOLS-$(CONFIG_LIBMYSOFA) += sofa2wavs
+TOOLS-$(CONFIG_ZLIB) += cws2fws
+
+tools/target_dec_%_fuzzer.o: tools/target_dec_fuzzer.c
+	$(COMPILE_C) -DFFMPEG_DECODER=$*
+
+tools/target_bsf_%_fuzzer.o: tools/target_bsf_fuzzer.c
+	$(COMPILE_C) -DFFMPEG_BSF=$*
+
+tools/target_dem_%_fuzzer.o: tools/target_dem_fuzzer.c
+	$(COMPILE_C) -DFFMPEG_DEMUXER=$* -DIO_FLAT=0
+
+tools/target_dem_fuzzer.o: tools/target_dem_fuzzer.c
+	$(COMPILE_C) -DIO_FLAT=1
+
+tools/target_io_dem_fuzzer.o: tools/target_dem_fuzzer.c
+	$(COMPILE_C) -DIO_FLAT=0
+
+tools/venc_data_dump$(EXESUF): tools/decode_simple.o
+tools/scale_slice_test$(EXESUF): tools/decode_simple.o
+
+OUTDIRS += tools
+
+clean::
+	$(RM) $(CLEANSUFFIXES:%=tools/%)
+
+-include $(wildcard tools/*.d)