/usr/include/d/4.9/std/c/ is in libphobos-4.9-dev 4.9.3-13ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/d/4.9/std/c/fenv.d
/usr/include/d/4.9/std/c/freebsd/
/usr/include/d/4.9/std/c/freebsd/socket.d
/usr/include/d/4.9/std/c/linux/
/usr/include/d/4.9/std/c/linux/linux.d
/usr/include/d/4.9/std/c/linux/linuxextern.d
/usr/include/d/4.9/std/c/linux/pthread.d
/usr/include/d/4.9/std/c/linux/socket.d
/usr/include/d/4.9/std/c/linux/termios.d
/usr/include/d/4.9/std/c/linux/tipc.d
/usr/include/d/4.9/std/c/locale.d
/usr/include/d/4.9/std/c/math.d
/usr/include/d/4.9/std/c/osx/
/usr/include/d/4.9/std/c/osx/socket.d
/usr/include/d/4.9/std/c/process.d
/usr/include/d/4.9/std/c/stdarg.d
/usr/include/d/4.9/std/c/stddef.d
/usr/include/d/4.9/std/c/stdio.d
/usr/include/d/4.9/std/c/stdlib.d
/usr/include/d/4.9/std/c/string.d
/usr/include/d/4.9/std/c/time.d
/usr/include/d/4.9/std/c/wcharh.d
/usr/include/d/4.9/std/c/windows/
/usr/include/d/4.9/std/c/windows/com.d
/usr/include/d/4.9/std/c/windows/stat.d
/usr/include/d/4.9/std/c/windows/windows.d
/usr/include/d/4.9/std/c/windows/winsock.d