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)
http://en.wikipedia.org/wiki/University_of_Illinois/NCSA_Ope...
Looks a lot like a 3-clause BSD, but it's a cross between MIT and BSD. The point on LGPL is that if GCC were LGPL, Apple would be able to link it to Xcode.
LGPL would be fine for that.