hwclock: add --systz option to set system clock from itself

hwclock: add --systz option to set system clock from itself

Since the system clock time is already set from the hardware clock by the
kernel (when compiled with CONFIG_RTC_HCTOSYS), there's no particular need to
read the hardware clock again.

This option sets the system clock using itself as a reference if the
hardware clock was in local time.  The resulting system clock time
is in UTC, with the kernel timezone set to the difference.

[kzak@redhat.com: - fix the condition that controls read_adjtime() call]

Signed-off-by: Scott James Remnant <scott@ubuntu.com>
Signed-off-by: Karel Zak <kzak@redhat.com>