To aid others in getting a leg up on building libc++, we've released a snapshot of our libc++abi which libc++ links to. This has only been tested on Mac OS 10.6. This code carries the GPL2 license. This is not part of the llvm project, nor will there be regular updates to this library.
http://home.roadrunner.com/~hinnant/libcppabi.zip
-Howard