user/liborcus: fix corner case build error
[06:14] <@awilfox> /usr/lib/gcc/powerpc64-foxkit-linux-musl/8.3.0/../../../../powerpc64-foxkit-linux-musl/bin/ld: liborcus/.libs/liborcus-0.15.so: undefined reference to `orcus::json_map_tree::node_child_default_position' [06:14] <@awilfox> collect2: error: ld returned 1 exit status [06:14] <@awilfox> make[3]: *** [Makefile:1421: orcus-css-dump] Error 1