You should not put built/bin on your PATH. This makes the installer use the copy of interrogate that is in there, which will not work because it is compiled for a different architecture.
Instead, leave your system Panda3D SDK somewhere on the PATH. Just keep in mind that interrogate depends on other Panda3D libraries in dtool that, when added to the DYLD_LIBRARY_PATH, may interfere with your build.
Also keep in mind that the “dtool” tree contains libraries that need to be linked into other Panda libraries later in the process, so compiling the “dtool” tree for Mac OS X instead of iPhoneOS to solve the interrogate issue will not work. You really need two separate versions of Panda3D; the iPhoneOS ones you are building, and the one that is used by utilities that need to be run during the build (mainly interrogate), which could simply be an existing installation of the Panda3D SDK for Mac OS X.
For the record, I do not recommend compiling with an optimize level of 1 when building for such a low-end machine; it’s usually best to squeeze out every drop of performance to make it run decently. Optimize 1 will be exceedingly slow on the iPhone.
The errors you’re getting indicate that the _igate.o file for libp3express didn’t get properly linked in. Can you show me the compilation steps for a clean build of the express directory?