But make failed because of 3 warnings in /lib/netplay.c. In lines 1620, 1251 and 1530 the function SDLNet_TCP_Send() is given a const char*, but the function seems to remove the const qualifier:
msgid "passing argument %d of %qE discards qualifiers from pointer target type"
When I add a typecast to char* (SDLNet_TCP_Send(tcp_socket, (char*)"list", 5); ) it compiles.
Hooray for const correctness! ::)

