I'm building zabbix for openwrt which uses uclibc. The architecture is correctly identified by Zabbix as Linux. In the file src/libs/zbxsysinfo/linux/cpu.c it is assumed that the getloadavg() function is always available in Linux, checks (#ifdef HAVE_GETLOADAVG) have been removed.

getloadavg() is not available in uclibc, so I'd suggest you put those checks back in otherwise it doesn't compile for uclibc. Using cpu.c from the unknown arch dir works for me.