cpu.c broken for Solaris

The addition of #ifdef HAVE_PROC_LOADAVG breaks reporting of cpu load averages. This has not to be added at configuration time
and there is no /proc/loadavg necessary for getloadavg to work.

Furthermore SYSTEM_CPU_UTIL will just return "Not supported" for unknown reasons. It should give more details about what is not working (Permission ? Call failed ? Wrong parameters ? Bug in function ?). The most important CPU indicator "idle" is not usable by Zabbix and has never worked even in the newest 1.5.x series. How was the testing done ?