/usr/include/GNUstep/MDKit is in gworkspace.app 0.9.3-1+b2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/include/GNUstep/../../lib/GNUstep/Frameworks/MDKit.framework/Headers
/usr/include/GNUstep/../../lib/GNUstep/Frameworks/MDKit.framework/Headers