Force DOS users to enable memalign hack when needed,

the same way it's done for MinGW.

Originally committed as revision 12299 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1270,7 +1270,6 @@ case $targetos in
         SHFLAGS='-shared -Wl,--enable-auto-image-base'
         ;;
     *-dos|freedos|opendos)
-        enable memalign_hack
         disable ffplay ffserver vhook
         disable $INDEV_LIST $OUTDEV_LIST
         network_extralibs="-lsocket"