If you are a Cocoa or Cocoa Touch developer, you may have attempted to use features such as properties in GNUstep, only to be surprised that these don't seem to be supported. This is because these are Objective-C 2.0 features.
To get the new features, the only way is to use a different compiler called clang. You may have seen this compiler used in newer releases of Xcode. This is a compiler that targets a virtual machine called LLVM before producing native code.
UPDATE May 4th 2011: GCC 4.6 has got the Objective-C 2.0 treatment, and since Debian includes GCC 4.6, I'd recommend you to try compiling your software that way. Not because it's a better compiler — I have no idea which one works better — but because it's there. Also, consider compiling GNUstep from trunk using GCC 4.6; it's rather easy to do. (CC=gcc-4.6 ./configure, whenever compiling a component of GNUstep).
Let's presume you managed to run an Objective-C program with GNUstep; that is, let's presume you are aware of Project Center, or GNUmakefiles. If you are didn't use GNUmakefiles, you should know that Project Center generates these in order to build your app.
Now you want to switch to clang, and you want to do so on your favorite operating system, Debian GNU/Linux.