configure: FFmpeg hwaccel requires libavcodec < 57.10.100

Since n2.9-dev-1400-g31741ae, the VLC avcodec plug-in will fail to
initialize hwaccel. This is by FFmpeg design.

configure.ac

@@ -2353,11 +2353,18 @@ AM_CONDITIONAL([HAVE_VAAPI_X11], [test "${have_vaapi_x11}" = "yes"])
 
 have_avcodec_vaapi="no"
 AS_IF([test "${have_vaapi}" = "yes" -a "${have_avcodec}" = "yes"], [
+  case "${avfork}" in
+    ffmpeg)
+      PKG_CHECK_EXISTS([libavcodec >= 57.10.100], [
+        AC_MSG_ERROR([VA API requires FFmpeg libavcodec < 57.10 or libav.])
+      ])
+      ;;
+  esac
   VLC_SAVE_FLAGS
   CPPFLAGS="${CPPFLAGS} ${AVCODEC_CFLAGS}"
   CFLAGS="${CFLAGS} ${AVCODEC_CFLAGS}"
   AC_CHECK_HEADERS([libavcodec/vaapi.h], [
-    AC_MSG_NOTICE([VAAPI acceleration activated])
+    AC_MSG_NOTICE([VA API acceleration activated])
     have_avcodec_vaapi="yes"
   ],[
     AS_IF([test -n "${enable_libva}"], [
@@ -2380,6 +2387,13 @@ have_avcodec_dxva2="no"
 AS_IF([test "${enable_dxva2}" != "no"], [
   if test "${SYS}" = "mingw32"; then
   AS_IF([test "x${have_avcodec}" = "xyes"], [
+    case "${avfork}" in
+      ffmpeg)
+        PKG_CHECK_EXISTS([libavcodec >= 57.10.100], [
+          AC_MSG_ERROR([DXVA2 requires FFmpeg libavcodec < 57.10 or libav.])
+        ])
+        ;;
+    esac
     AC_CHECK_HEADERS(dxva2api.h,
       [
         AC_CHECK_HEADERS(libavcodec/dxva2.h, [
@@ -3076,7 +3090,11 @@ have_avcodec_vdpau="no"
 AS_IF([test "${have_vdpau}" = "yes" -a "${have_avcodec}" = "yes"], [
   case "${avfork}" in
     libav) av_vdpau_ver="55.26.0" ;;
-    ffmpeg) av_vdpau_ver="55.42.100" ;;
+    ffmpeg) av_vdpau_ver="55.42.100"
+      PKG_CHECK_EXISTS([libavcodec >= 57.10.100], [
+        AC_MSG_ERROR([VDPAU requires FFmpeg libavcodec < 57.10 or libav.])
+      ])
+      ;;
   esac
   PKG_CHECK_EXISTS([libavutil >= 52.4.0 libavcodec >= ${av_vdpau_ver}], [
     have_avcodec_vdpau="yes"