I'm not a developer, but perhaps I can help you aim for the right direction.
From the Slackware FTP server
gcc-objc: gcc-objc (Objective-C support for GCC)
gcc-objc: Objective-C support for the GNU Compiler Collection.
gcc-objc: This package contains those parts of the compiler collection needed to
gcc-objc: compile code written in Objective-C. Objective-C was originally
gcc-objc: developed to add object-oriented extensions to the C language, and is
gcc-objc: best known as the native language of the NeXT computer.
gcc-objc: The base gcc package is also required.
So, my question is, do you only have a base install of GCC (C and possibly C++)? Without knowing more info - such as, are you actually running Fedora 12 - it's impossible for anyone to give you more of an answer
. Since I don't personally run Fedora, I have a minimal understanding of their package tools. Presumably, you need to install the missing add-ons for GCC in your installation of Fedora.
And finally, have you read what the GNUstep site has to say
? No one else is going to say it better.