Use coff as objformat for dos.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@16525 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

configure

@@ -1497,7 +1497,7 @@ case $target_os in
         disable $INDEV_LIST $OUTDEV_LIST
         network_extralibs="-lsocket"
         EXESUF=".exe"
-        objformat="win32"
+        objformat="coff"
         enable dos_paths
         ;;
     linux)