AC_DEFUN([AC_EXPAND], [
  test "x$prefix" = xNONE && prefix="$ac_default_prefix"
  test "x$exec_prefix" = xNONE && exec_prefix='${prefix}'
  ac_expand=[$]$1
  test "x$ac_expand" = xNONE && ac_expand="[$]$2"
  ac_expand=`eval echo [$]ac_expand`
  $3=`eval echo [$]ac_expand`
])