cmake_build_dir$ more CMakeCache.txt
...

//Path to a file.
Boost_INCLUDE_DIR:PATH=/home/dp/projects/wesnoth/lib/include/
...

$ $ ll /home/dp/projects/wesnoth/lib/include/boost/unordered_map.hpp
-rw-r--r-- 1 dp staff 550 2011-04-20 16:13 /home/dp/projects/wesnoth/lib/include/boost/unordered_map.hpp

---

Compilation error:

...
                 from /home/dp/projects/wesnoth/src/wesnoth/src/arrow.cpp:21:
/home/dp/projects/wesnoth/src/wesnoth/src/map_location.hpp:27:35: error: boost/unordered_map.hpp: No such file or directory
In file included from /home/dp/projects/wesnoth/src/wesnoth/src/unit.hpp:23,
dp
...