llvm/clang: Move to tip of 3.8 branch
llvm/clang: Move to tip of 3.8 branch

Make the SRCREV, PV, BRANCH weak assignments
so they can be overridden

Signed-off-by: Khem Raj <729d64b6f67515e258459a5f6d20ec88b2caf8df@gmail.com>

kraj/meta-clang,dsacre/meta-clang,kraj/meta-clang,kraj/meta-clang