I have now uninstalled and re-installed XCode-312 three times, both by running the uninstaller and by just deleting /Deveoper/ and every time I run the installer it tells me it's doing an "upgrade" and fails to install diagnostics.pm (wherever that's supposed to go) and also doesn't create links for, e.g., /usr/bin/gcc (though gcc is in /Developer/usr/bin/).
So how do I un-screw things?
(And, hey, Apple -- "genius" idea not to ship diagnostics.pm in the standard, non-XCode Perl install.)
Update: I gave up and installed the newer XCode. It's so frustrating that I have to wait for a 4.7 GB download just to have a functional gcc and perl... I will never run XCode on this machine (let alone the iPhone cross-compiler!), but there's no other way to get the parts that everything else depends on.