Some compilers will silently ignore -O when -g is specified.  If yours does,
edit the Makefile and remove -g.

Here are a list of programs that will NOT work with slirp:

- rlogin.  Infact, most "r"-commands won't work because they need to bind()
  a privileged port

- talk client.  Doesn't work yet, but I am working on emulating it (it's not
  trivial)

