I had a compilation error when compiling on the new OS X lion - it boiled down to /usr/include/unwind.h being different than the standard GCC version.
In particular, _Unwind_Exception_Class and _Unwind_Ptr, are not declared, but where they are referenced previously, uint64_t and uintptr_t are used instead. I've not done any form of extensive testing, but the attached patch seems to suffice to make it compile.
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I am not sure, but the preprocessor check for __llvm__ may need to be stricter, in the sense that maybe llvm-gcc on linux probably uses the standard GCC unwind.h.
Tai Chi Minh Ralph Eastwood