configure: allow 'none' as target OS

Originally committed as revision 21732 to svn://svn.ffmpeg.org/ffmpeg/trunk

diff --git a/configure b/configure
index e4eabb1..548c16a 100755 (executable)
--- a/configure
+++ b/configure
@@ -2217,7 +2217,8 @@ case $target_os in
         ;;
     gnu)
         ;;
-
+    none)
+        ;;
     *)
         die "Unknown OS '$target_os'."
         ;;