[PATCH] systemd compatibility

[Davide Cavalca]

Hi,

here's a couple of patches to improve busybox compatibility with
systemd:
- 0001 adds a minimal sd-daemon implementation to libbb
- 0002 implements socket activation for syslogd
- 0003 implements hwclock --systz
- 0004 adds example systemd units for a number of busybox applets

The sd-daemon stuff is a stripped-down version of the reference
implementation shipped with systemd, with only the bare minimum required
to make syslogd work (i.e. AF_UNIX socket activation). hwclock --systz
is based on the util-linux-ng implementation.

make bloatcheck for syslogd:

function                                             old     new   delta
sd_listen_fds                                          -     287    +287
.rodata                                           145677  145844    +167
xsystemd_unix_socket                                   -      88     +88
create_socket                                        154     175     +21
------------------------------------------------------------------------------
(add/remove: 3/0 grow/shrink: 2/0 up/down: 563/0)             Total: 563
bytes
   text	   data	    bss	    dec	    hex	filename
 921266	   4114	   9536	 934916	  e4404	busybox_old
 922241	   4114	   9536	 935891	  e47d3	busybox_unstripped

and for hwclock:

function                                             old     new   delta
hwclock_main                                         345     461    +116
.rodata                                           145902  145945     +43
packed_usage                                       27401   27424     +23
static.hwclock_longopts                               53      61      +8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 4/0 up/down: 190/0)             Total: 190
bytes
   text	   data	    bss	    dec	    hex	filename
 922188	   4114	   9568	 935870	  e47be	busybox_old
 922347	   4114	   9568	 936029	  e485d	busybox_unstripped

Please review - this is my first contribution to busybox, so let me know
if I've done something stupid :)

Regards,
Davide
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