Take anything I've got with a heaping pile of salt, I'm not the best compiler and linker of C projects in the world, but I think I've found a minor issue when compiling in png support.
This is all on my 10.5.8 OS X computer.
I've been compiling devIL 1.7.8 and trying to link to libpng. My installer for libpng installed two versions, libpng12 and libpng14. devIL attempted to use 12 first, but could not find the _png_set_longjump_fn symbol at runtime, and failed out of its make test for png. Figuring you needed a later version, I deleted the libpng12 .a and .dylib files (and all references to them), and reran configure. This caused the new libIL library to reference libpng14 as I'd hoped.
Unfortunately, libIL also made use of png_sig_check, which was deprecated, and as of the version of libpng14 I downloaded, has been removed from the library entirely.
My solution: Change line 108 of il_png.c from png_check_sig(Signature,8); to png_sig_cmp(Signature,0,8). As far as I can tell, this works properly. (Doesn't fail out with dyld error messages anyway.
Thanks for awesome image loading library, hope I've found a good bug for you.