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The *rtc* translator implements a real-time clock driver. It can be used to add
the `rtc` device files, with those files, we can access the underlying
real-time clock using `ioctl()`. The description of `ioctl()` can be found
[here](https://www.gnu.org/software/libc/manual/html_node/IOCTLs.html).

The operation macros are required to access the real-time clock. They are
defined as `RTC_*` in `hurd/rtc.h`.

The `hwclock` command from `util-linux` can use the `rtc` device files to
access the real-time clock devices.

# Usage Example
Setup a `rtc` device file in `/tmp`:

    settrans -c /tmp/rtc /hurd/rtc

Read the time value through the `rtc` device file:
 
    int fd = open("/tmp/rtc", O_RDONLY);
    struct rtc_time time;
    ioctl(fd, RTC_RD_TIME, &time);