Getting Ruby 1.8.4 to pass 'make test-all' on MacOS X can be tricky. Here's a list of things which may help:
* Set your GCC back to version 3.3. This cleans up a lot of warning messages, and may prevent bugs caused by GCC 4.0.
sudo gcc_select 3.3
* Disable your firewall (if you're on a safe network!) before running 'make test-all', and turn it back on again afterwards. The Ruby networking tests assume they can listen on addresses other than 127.0.0.1, which isn't a safe assumption under MacOS X. You can disable your firewall under "System Preferences" > "Sharing".
* Run 'make install' *before* running 'make test-all'. The test suites rely on an installed copy of Ruby to run.
Hope this helps! Some of these tips will apply to other platforms, too.
Cheers,
Eric