configure: Fix required version checks for lavf and swscale

configure

@@ -1102,10 +1102,10 @@ if [ "$swscale" = "auto" ] ; then
     [ -z "$SWSCALE_LIBS" ] && SWSCALE_LIBS="-lswscale -lavutil"
 
     if cc_check "libswscale/swscale.h" "$SWSCALE_CFLAGS $SWSCALE_LIBS" "sws_init_context(0,0,0);" ; then
-        if cpp_check "libavutil/pixdesc.h" "$SWSCALE_CFLAGS $SWSCALE_LIBS" "defined(AV_PIX_FMT_FLAG_RGB)" ; then
+        if cc_check "libavutil/pixdesc.h" "$SWSCALE_CFLAGS $SWSCALE_LIBS" "AVComponentDescriptor x; x.depth = 8;" ; then
             swscale="yes"
         else
-            echo "Warning: AV_PIX_FMT_FLAG_RGB is missing from libavutil, update for swscale support"
+            echo "Warning: libswscale is too old"
         fi
     fi
 fi
@@ -1124,12 +1124,16 @@ if [ "$lavf" = "auto" ] ; then
     fi
 
     if cc_check libavformat/avformat.h "$LAVF_CFLAGS $LAVF_LIBS" "av_register_all();" ; then
-        if [ "$swscale" = "yes" ]; then
+        if cc_check libavcodec/avcodec.h "$LAVF_CFLAGS $LAVF_LIBS" "avcodec_send_packet(0,0);" ; then
             lavf="yes"
         else
-            echo "Warning: libavformat is not supported without swscale support"
+            echo "Warning: libavformat is too old"
         fi
     fi
+    if [ "$lavf" = "yes" -a "$swscale" = "no" ]; then
+        echo "Warning: libavformat is not supported without swscale support"
+        lavf="no"
+    fi
 fi
 
 if [ "$ffms" = "auto" ] ; then