I bet you'll want to install the Dev Tools. Between installing 10.1 and the new Dev Tools, I noticed that a lot of functions from the command line were broken or messed up. I'm also seeing that a lot of what's in /usr/bin was updated (or at least touched) when I installed the Dev Tools.
I just tried to remake zlib 1.1.3 and it finished without a problem.
Note that these are available for free from Apple Developer Connection (http://connect.apple.com/). You need to create an account if you don't have one yet, but you do not need one of the paid memberships to access the Dev Tools. The download is 187 MB, though, so you'll probably want a fast connection!