Fixes when including with CMake add_subdirectory()

[ahogen]

With the included fixes, I can now include this repository as a git submodule of my own project and include it in my build directly using add_subdirectory().

my_project/external/CMakeLists.txt

set(CERBERUS_CPP_FIND_YAML_CPP OFF)
add_subdirectory(cerberus-cpp EXCLUDE_FROM_ALL)

add_subdirectory(yaml-cpp EXCLUDE_FROM_ALL)
target_include_directories(yaml-cpp SYSTEM INTERFACE
    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/yaml-cpp/include>
)

my_project/src/CMakeLists.txt

add_executable(main main.cpp)
target_link_libraries(main
    PRIVATE
        yaml-cpp
        cerberus-cpp
)

[dokempf]

This variable name does not match the option defined in line 11. Also: Why is this even needed? We do need to find yaml-cpp anyway.

[ahogen]

variable name does not match the option defined in line 11

Oops yep old variable name that I later made simpler. Fixed.

Also: Why is this even needed? We do need to find yaml-cpp anyway.

Cerberus does not need to find yamp-cpp when my project is including both repos as submodules/subdirectories, as indicated in the MR description. cerberus-cpp can use the CMake target yaml-cpp directly. I do not have nor do I want to install yaml-cpp from a DEB/RPM package.

[dokempf]

LGTM!