Add Hurd to OS list and disable dv1394 in the Hurd case.

patch by Andres Mejia, mcitadel gmail com


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@18938 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -1697,6 +1697,9 @@ case $target_os in
         ;;
     gnu/kfreebsd)
         ;;
+    gnu)
+        disable dv1394
+        ;;
 
     *)
         die "Unknown OS '$target_os'."