[CMake] CMake fails to find sys/event.h on FreeBSD 10.2

[Klemen Ferjančič]

FreeBSD 10.2-STABLE
CMake 3.3.1

Our projects needs kqueue which means that sys/types.h and sys/event.h
need to be found. Googling around also revealed that event.h is not self
inclusive but depends on type.h. Not sure if that has to do with
anything though.

CMakeLists.txt:
check_include_file_cxx(sys/types.h HAVE_SYS_TYPES_H)
if (HAVE_SYS_TYPES_H)
check_include_file_cxx(sys/event.h HAVE_SYS_EVENT_H)
endif()

Result:
cmake -G "Unix Makefiles" -H./ -B./build
-- Looking for C++ include sys/types.h
-- Looking for C++ include sys/types.h - found
-- Looking for C++ include sys/event.h
-- Looking for C++ include sys/event.h - not found

Both files exist in /usr/include/sys. Tried with check_include_file too
but same problem.

Can anyone tell me if I am doing something wrong and any idea why
event.h is not found?