Other GNU/Linux compilation tips

When compiling, you might get the following error: In file included from ud_socket.c:18: ud_socket.h:12: warning: 'struct ucred' declared inside parameter list ud_socket.h:12: warning: its scope is only this definition or declaration, which is probably not what you want ud_socket.c:56: warning: 'struct ucred' declared inside parameter list

To fix it: