In the 4.9.0 development release, the clock plugin fails to compile with the following error:

gmake[4]: Entering directory `/storage/build/xfce410/xfce4-panel-4.9.0/plugins/clock'
  CC     libclock_la-clock.lo
clock.c:907: error: syntax error before "info"
clock.c: In function `clock_plugin_timeout_expired':
clock.c:909: error: `info' undeclared (first use in this function)
clock.c:909: error: (Each undeclared identifier is reported only once
clock.c:909: error: for each function it appears in.)
gmake[4]: *** [libclock_la-clock.lo] Error 1

Basically, Solaris knows nothing of sigval_t. I was able to work around this with the addition of the following to plugins/clock/clock.c:

typedef union sigval sigval_t;

but I have no idea what a correct fix would look like.