If you’ve been having problems compiling various Unix packages on OS X 10.5.4, and that your compile run fails mysteriously with something like:
i686-apple-darwin9-gcc: /usr/X11/lib/libpng18.104.22.168.dylib: No such file or directory
One strange yet very likely explanation: your libtool archive file /usr/X11/lib/libpng12.la is lying about the location of the shared library for libpng12 — namely, that a file called /usr/X11/lib/libpng22.214.171.124.dylib exists and should be used for linking against libpng12. However, if you actually look in /usr/X11/lib, no such file exists – perhaps you might have libpng.0.24.0.dylib, but not .26. Therefore, packages that make use of this incorrect libtool archive metadata are suitably confused, causing the compiler to bail out when trying to link against this non-existent file.
Since libtool archive (.la) files are text-based, you can open it up in emacs. The quick and dirty fix to this is to simply change the offending library_names and the current and age properties to the correct numbers. In my case, the libpng sitting in /usr/X11/lib was .24, and so I string-replaced all the values in those three properties from 26 to 24. The compilation then proceeded normally.
The long term solution, of course, is to track down what put a wrong .la file there in the first place. I suspect Xcode 3.1 and Mac OS X SDK 10.5, which shipped with the latest iPhone SDK.
In the comments section, I’ve been informed that the X11SDK package in Xcode 3.1 in the culprit. Thanks Anonymous!