Project 'class_loader' specifies '/include' as an include dir about class_loader

[jianghui-lin]

If you look at the error porint in the problematic cmke file(class_loaderConfig.cmake), there is an unexpected path in the _include_dirs variable -- '/include' which cmake complain can't find it under '/' path.
And if check 'which gcc' is '/bin/gcc' rather than '/usr/bin/gcc', that means your bin path is misordered in $PATH env, and you can try to reorder it with e.g 'export PATH="/usr/bin/:/bin/:/sbin:$PATH"', and try build ROS again.

[davidfreina]

Had the same bug and I have a temporary fix for it.
Go to the ~/.cache/yay/ros-melodic-class-loader/src/class_loader-0.4.1/ folder and rename the 'include' folder to '/include'.
This worked for me under ArchLinux Kernel 5.9.8-zen1-1-zen.