Fix YAML include dirs cont.

[dennisklein]

Continuation of #909

[davidrohr]

This looks OK for the CMakeList, but the path is also used in fairtools/MCConfigurator/CMakeLists.txt, which I had to change as well in #909

[dennisklein]

also used in fairtools/MCConfigurator/CMakeLists.txt, which I had to change as well in #909

I saw, the variable should propagate downwards. I'll double check.

[davidrohr]

OK, you are right, since you overwrite the variable it will be OK.

[dennisklein]

Hm, I don't even see your case, both my system and non-system installations have even conflicting include dirs^^

╭─dklein@gamma ~/projects/FairRoot ‹ruby-2.6.0› ‹davidrohr/PR2*›
╰─➤  grep YAML_CPP_INCLUDE_DIR /usr/lib64/cmake/yaml-cpp/yaml-cpp-config.cmake
set(YAML_CPP_INCLUDE_DIR "/usr/include/yaml-cpp")
╭─dklein@gamma ~/projects/FairRoot ‹ruby-2.6.0› ‹davidrohr/PR2*›
╰─➤  grep -B1 YAML_CPP_INCLUDE_DIR /home/dklein/fairsoft/dev_5b980cf/lib64/cmake/yaml-cpp/yaml-cpp-config.cmake
get_filename_component(YAML_CPP_CMAKE_DIR "${CMAKE_CURRENT_LIST_FILE}" PATH)
set(YAML_CPP_INCLUDE_DIR "${YAML_CPP_CMAKE_DIR}/../../../include")

Since we include <yaml-cpp/yaml.h> the include path my system installation (Fedora 30) provides is not even effective... weird packaging... (both installations claim to be v0.6.2)

[dennisklein]

Anyways, coming back to the fairtools/MCConfigurator/CMakeLists.txt, I checked the absolute path is used. Merging.

[davidrohr]

Hm, I have 0.6.2 as well. the YAML CMake Config file /usr/lib64/cmake/yaml-cpp/yaml-cpp-config.cmake sets
set(YAML_CPP_INCLUDE_DIR "${YAML_CPP_CMAKE_DIR}/../../../include")
which becomes /usr/include (with some [something]/../). If that is used as system include path (which happened in fairtools/MCConfigurator/CMakeLists.txt, it breaks the compilation.