openbsd编译mysql 失败，求教。

解压 mysql-5.5.20.tar.gz 后cd进去
cmake . 时出现以下错误提示。
CMake Error at cmake/boost.cmake:81 (MESSAGE):
You can download it with -DDOWNLOAD_BOOST=1 -DWITH_BOOST=<directory>
This CMake script will look for boost in <directory>. If it is not there,
it will download and unpack it (in that directory) for you.
If you are inside a firewall, you may need to use an http proxy:
export http_proxy=http://example.com:80
Call Stack (most recent call first):
cmake/boost.cmake:238 (COULD_NOT_FIND_BOOST)
CMakeLists.txt:491 (INCLUDE)
求解，非常感谢。