/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/ is in libgphobos-6-dev-i386-cross 6.4.0-17ubuntu1cross1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/dlfcn.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/execinfo.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/cdefs.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/elf.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/elf32.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/elf64.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/elf_common.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/event.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/link_elf.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/sys/mman.d
/usr/lib/gcc-cross/i686-linux-gnu/6/include/d/core/sys/freebsd/time.d