/usr/include/GNUstep/AdunKernel is in adun.app 0.81-6.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/GNUstep/../../lib/GNUstep/Frameworks/AdunKernel.framework/Headers
/usr/include/GNUstep/../../lib/GNUstep/Frameworks/AdunKernel.framework/Headers