The OS X Developer Tools installer is (or should be) in
Just install the whole package.
Once you've done that, the program "m4" should be in /usr/bin, and /usr/bin should always be in your $PATH, so from any Terminal window you should be able to run the update script and get the expected messages.
I don't know what the "Bad file descriptor" stuff is all about. It doesn't sound related to your missing DevTools. After you've installed the DevTools and rerun update, check for these messages again. If they're still happening, come back here, and perhaps someone will be able to help.
The gethostbyaddr failure is more-or-less expected: your machine appears to be behind a NAT firewall. See the last page of the article for some pointers on dealing with this. Since you're more interested in sending that receiving mail, the NAT shouldn't be a terrible issue, but (as the article says) make very sure that the mail you send out can be replied to (arriving in some other, "real" mail box). That can be done by providing a "Reply-To:" header pointing to the real box, or by providing the real box as "From:".