The result? Clang has this warning, GCC doesn't. I think it is easy to find many examples like this.
Improving Clang/LLVM is relatively easy. Working on GCC requires incredibly amounts of knowledge, motivation, persistence and social maneuvering to get patches reviewed and approved.
One of the points that Delesley made is that the code was integrated into trunk immediately in LLVM, whereas in GCC it was languishing in a branch that would take super-human persistence during several months to get reviewed and accepted.
In fact, it is likely that Google will work less closely with GCC, as more of their engineers rely on LLVM.