Hi,
All of the installation steps involve running ./configure && make && sudo -E make install. You will need to install some dependencies first in order to be able to build various GNUstep components, e.g. gnustep-base. This is all documented in a couple of places around the web (except we no longer use Subversion, so adjust the checkout commands and URLs). The order in which to install out code:
First install gnustep-make.
After installing gnustep-make, you can install gnustep-base.
After installing libs-xcode, you can install buildtool.
However, this won't be of much assistance: GNUstep's language of choice is Objective-C, and Swift is not currently a supported language. This also means that libs-xcode does not currently understand how to build Swift.
If you look at its PBXFileReference you'll see that it only understands how to talk to the output of `gnustep-config --variable=CC`.
Sorry.