Fix compilation on FreeBSD 4

Grarpamp reports on tor-talk that Tor 0.2.2 doesn't build on freebsd 4, whereas 0.2.1 did. I've got a partial patch series at branch called "gcc-295-fix" in my public repository; I should get him to test it, test it more on other platforms, and make sure that it covers all the issues he mentioned in his emails.