openjfx: FTBFS with ffmpeg 5.0

Imported from Debian bug http://bugs.debian.org/1004638:

openjfx FTBFS with ffmpeg 5.0 (available in experimental):
| gcc -fPIC -Wformat -Wextra -Wformat-security -fstack-protector -Werror=implicit-function-declaration -Werror=trampolines -fbuiltin -DHAVE_STDINT_H -DLINUX -DGST_DISABLE_LOADSAVE -DGSTREAMER_LITE -ffunction-sections -fdata-sections -Wdate-time -D_FORTIFY_SOURCE=2 -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>/modules/javafx.media/src/main/native/gstreamer/projects/linux/avplugin=. -fstack-protector-strong -Wformat -Werror=format-security -Wall -msse2 -I../../../plugins -I../../../plugins/av -I../../../gstreamer-lite/gstreamer -I../../../gstreamer-lite/gstreamer/libs -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/x86_64-linux-gnu -c ../../../plugins/av/videodecoder.c -o /<<PKGBUILDDIR>>/modules/javafx.media/build/native/linux/Release/obj/plugins/avplugin/av/videodecoder.o
| In file included from /usr/include/glib-2.0/glib/gthread.h:32,
| from /usr/include/glib-2.0/glib/gasyncqueue.h:32,
| from /usr/include/glib-2.0/glib.h:32,
| from ../../../gstreamer-lite/gstreamer/gst/gst.h:27,
| from ../../../plugins/av/decoder.h:29,
| from ../../../plugins/av/decoder.c:26:
| ../../../plugins/av/decoder.c: In function ‘basedecoder_get_type’:
| /usr/include/glib-2.0/glib/gatomic.h:113:5: warning: argument 2 of ‘__atomic_load’ discards ‘volatile’ qualifier [-Wincompatible-pointer-types]
| 113 | __atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
| | ^~~~~~~~~~~~~
| /usr/include/glib-2.0/glib/gthread.h:260:7: note: in expansion of macro ‘g_atomic_pointer_get’
| 260 | (!g_atomic_pointer_get (location) && \
| | ^~~~~~~~~~~~~~~~~~~~
| ../../../plugins/av/decoder.c:58:9: note: in expansion of macro ‘g_once_init_enter’
| 58 | if (g_once_init_enter (&gonce_data))
| | ^~~~~~~~~~~~~~~~~
| ../../../plugins/av/decoder.c:64:16: warning: cast between incompatible function types from ‘void (*)(void *)’ to ‘void (*)(void *, void *)’ [-Wcast-function-type]
| 64 | (GClassInitFunc) basedecoder_class_intern_init,
| | ^
| ../../../plugins/av/decoder.c:66:16: warning: cast between incompatible function types from ‘void (*)(BaseDecoder *)’ {aka ‘void (*)(struct _BaseDecoder *)’} to ‘void (*)(GTypeInstance *, void *)’ {aka ‘void (*)(struct _GTypeInstance *, void *)’} [-Wcast-function-type]
| 66 | (GInstanceInitFunc) basedecoder_init,
| | ^
| ../../../plugins/av/decoder.c: In function ‘basedecoder_init’:
| ../../../plugins/av/decoder.c:73:43: warning: unused parameter ‘self’ [-Wunused-parameter]
| 73 | static void basedecoder_init(BaseDecoder *self)
| | ~~~~~~~~~~~~~^~~~
| ../../../plugins/av/decoder.c: In function ‘basedecoder_class_init’:
| ../../../plugins/av/decoder.c:79:5: error: implicit declaration of function ‘avcodec_register_all’ [-Werror=implicit-function-declaration]
| 79 | avcodec_register_all();
| | ^~~~~~~~~~~~~~~~~~~~
| ../../../plugins/av/decoder.c: In function ‘basedecoder_open_decoder’:
| ../../../plugins/av/decoder.c:112:20: warning: assignment discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
| 112 | decoder->codec = avcodec_find_decoder(id);
| | ^
| ../../../plugins/av/decoder.c: In function ‘basedecoder_set_codec_data’:
| ../../../plugins/av/decoder.c:169:17: warning: ‘g_memdup’ is deprecated: Use 'g_memdup2' instead [-Wdeprecated-declarations]
| 169 | decoder->codec_data = g_memdup(info.data, info.size);
| | ^~~~~~~
| In file included from /usr/include/glib-2.0/glib.h:82,
| from ../../../gstreamer-lite/gstreamer/gst/gst.h:27,
| from ../../../plugins/av/decoder.h:29,
| from ../../../plugins/av/decoder.c:26:
| /usr/include/glib-2.0/glib/gstrfuncs.h:257:23: note: declared here
| 257 | gpointer g_memdup (gconstpointer mem,
| | ^~~~~~~~
| cc1: some warnings being treated as errors
| make[2]: *** [Makefile:81: /<<PKGBUILDDIR>>/modules/javafx.media/build/native/linux/Release/obj/plugins/avplugin/av/decoder.o] Error 1