Well, from the link you provided:
At the end of that process, you should have 2 ISO's located in this directory: (one each of the standard distro, and one devel edition, of either a 32-bit or 64-bit flavor depending on the host environment).
What you want to do is not so clear - are you compiling on a 64-bit machine but have a 3-bit machine set aside for smoothwall?
You can check if your compiler is multi-targeted - for example, compile a "hello_world.c" file using the compiler and "-m32" switch. You may need to install the 32-bit libs to be able to successfully link the program. Since the kernel does not link to any libraries, you can try to compile - not quite as normal, you need to make sure -m32 is supplied.
However, to make sure the binary is compatible with your intended system, it is best to set up a cross-compiler for the job - you need to put the 32-bit libs for your target system somewhere and set up the cross-compiler environment to use/link to them.