Rolling v8/buildtools to 5fc8d3943e163ee627c8af50366c700c0325bba2

Rolling v8/tools/clang to 6ab82bf7484ae7c06316c095e93b8b0dc6ea806a

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

Review URL: https://codereview.chromium.org/1388043002

Cr-Commit-Position: refs/heads/master@{#31118}