ktorrent proper doesn't depend on avahi, but it has an optional plugin that does, and by default the build system checks to see if avahi is present. There's an old Gentoo patch that I think is intended to provide support for explicitly disabling avahi (thus killing the check and just not building the plugin) via a configuration option, but it obviously won't apply if ktorrent has been converted to CMake. In other words, the warning is harmless if you're okay with autodetects, but we may be able to fix it anyway.