When building Zabbix 6.4 or pre-7.0 with Net-SNMP library in a custom location, it fails to use correct include paths. If Net-SNMP development package from the repository is installed, Zabbix will use header files from this package while linking will happen with the custom library. If package from the repository is not installed, building Zabbix will fail because it won't be able to find the header files.