The problem I was running into is solved but incase anyone else runs into this problem: Install with the "--force" option: cabal install --user --enable-documentation --ghc-pkg-option=--force gtk but if the build ends with "invalid argument" like this:
Linking /tmp/gtk-0.11.011162/gtk-0.11.0/dist/setup/setup ... Configuring gtk-0.11.0... setup: ./Graphics/UI/Gtk/General/IconTheme.chs: invalid argument Updating documentation index /home/tim/.cabal/share/doc/index.html
cabal: Error: some packages failed to install: gtk-0.11.0 failed during the building phase. The exception was: ExitFailure 1
Then you don't currently have your locale set to UTF-8. Set your localehttp://www.freebsd.org/doc/en/books/handbook/using-localization.htmlto UTF-8 then try again and it should work.