The svn llvm-gcc4 repository has now been successfully moved to svn://anonsvn.opensource.apple.com/svn/llvm/trunk. (This is to support tagging and future releases.)
You can do a fresh checkout;
svn co svn://anonsvn.opensource.apple.com/svn/llvm/trunk $mydir
or, I am told if you go to your llvm svn directory you can;
svn switch --relocate svn://anonsvn.opensource.apple.com/svn/llvm \
svn://anonsvn.opensource.apple.com/svn/llvm/trunk
Cheers,
-- Jim