I'm using the Unity 3D engine to build an iPhone app, and when I go to generate my Xcode project for compilation, it includes a few fairly large libraries: Mono.Security.dll.s, System.dll.s, System.Core.dll.s, etc.
I don't know if this question is really an Xcode question or a Unity question, but I'm trying to figure out why each of those libraries is being linked - which functions / classes are being referenced - ideally so that I can rewrite my code to remove as many of the dependencies as possible. Does anybody know a way to find this information out?
Are you using any external assemblies? If so you should get the source code for them and check what they are including. Sometimes it's possible to disable stuff in external assemblies to remove unneeded dependencies.
Go into the "project settings->player" menu in Unity and make sure that stripping level is set as high as possible. Stripping will attempt to swap System.Core with mscorlib, which doesn't include stuff like Linq.
A way to find out why a particular assembly is being included is to open up the references section of your MonoDevelop solution, and double-click on an assembly. This will open the assembly browser and you'll be able to get an idea of the namespaces that depend on a particular assembly.
This DLL stuff is added to project by Unity3D, Xcode has nothing to do with this. What version of Unity3D do you use? Try to tweak Optimization options in project settings (Inspector), especially 'Stripping'.