Yeah, but why bother? It's not like Apple has any reason to go LGPL (and actually, now that I looked it up Clang seems to use the same license as LLVM — which makes sense — and that's the University of Illinois/NCSA Open Source License not the 3-clauses BSD, which again makes sense considering LLVM got started at UIUC, so it's not even Apple who decided on the license of the LLVM suite and related tools, they got into LLVM years after the project started and just used the same license for the stuff they built on/around LLVM)