Add missing start-of-file descriptive comment.

	* io/futimens.c: Add missing start-of-file descriptive comment.
	* io/utime.c: Likewise.
	* misc/futimesat.c: Likewise.
	* misc/utimes.c: Likewise.
	* sysdeps/mach/hurd/futimesat.c: Likewise.
	* sysdeps/mach/hurd/utimes.c: Likewise.
	* sysdeps/posix/utime.c: Likewise.
	* sysdeps/posix/utimes.c: Likewise.
	* sysdeps/unix/sysv/linux/futimesat.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/futimesat.c: Likewise.
	* sysdeps/unix/sysv/linux/generic/utimes.c: Likewise.
	* sysdeps/unix/sysv/linux/utimes.c: Likewise.