/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/ is in libphobos-5-dev 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/execinfo.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/dyld.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/getsect.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/kern_return.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/loader.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/port.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/semaphore.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/mach/thread_act.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/pthread.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/sys/
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/sys/cdefs.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/sys/event.d
/usr/lib/gcc/x86_64-linux-gnu/5/include/d/core/sys/osx/sys/mman.d