Rolling v8/build to dfb08d9b315caad762d458ff3ed828e792913df3

Rolling v8/tools/clang to 6b75002bcce135ecacc1ff5a7fdb2f0647212198

TBR=machenbach@chromium.org,vogelheim@chromium.org,hablich@chromium.org

Review-Url: https://codereview.chromium.org/2354613004
Cr-Commit-Position: refs/heads/master@{#39524}