I'm trying to compile the latest from trunk on Mac OS X Lion. The build goes smooth, until linking. I get the following error:

Linking CXX executable gvbam.app/Contents/MacOS/gvbam
ld: warning: ignoring file /usr/local/lib/libz.dylib, file was built for unsupported file format which is not the architecture being linked (x86_64)
Undefined symbols for architecture x86_64:

Any idea why libz.dylib isn't supporting a x86_64 build? I haven't run in to this with any other projects.

Any help is greatly appreciated!

EDIT:

Just wanted to add that zlib is installed for x86_64 on my system

$ port -v installed zlib
The following ports are currently installed:
zlib @1.2.5_0 (active) platform='darwin 11' archs='x86_64'