Add video4linux2 detection to configure.

patch by Luca Abeni, lucabe72*at*email*dot*it

Originally committed as revision 4963 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1244,6 +1244,15 @@ ipv6=yes
 fi
 fi
 
+if test "$v4l2" = "yes"; then
+# check for video4linux2 --- V4L2_PIX_FMT_YUV420
+cat > $TMPC << EOF
+#include <linux/videodev.h>
+int dummy = V4L2_PIX_FMT_YUV420;
+EOF
+$cc -c -o $TMPE $TMPC 2> /dev/null || v4l2="no"
+fi
+
 case "`$cc -v 2>&1 | grep version`" in
     *gcc*)
         CFLAGS="-Wall -Wno-switch $CFLAGS"