Rolling v8/buildtools to dc487f429cb90cac92ec7a9cd9d49db13648064d

Rolling v8/tools/clang to c8d44a19b3bc34fe17b9b0361edebee4b9a70fdb

TBR=machenbach@chromium.org

Review URL: https://codereview.chromium.org/1151753004

Cr-Commit-Position: refs/heads/master@{#28530}