Update V8 DEPS.

Rolling v8/tools/clang to a8adb78c8eda9bddb2aa9c51f3fee60296de1ad4

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

Review URL: https://codereview.chromium.org/1717953002

Cr-Commit-Position: refs/heads/master@{#34179}

DEPS

@@ -29,7 +29,7 @@ deps = {
   "v8/test/test262/data":
     Var("git_url") + "/external/github.com/tc39/test262.git" + "@" + "738a24b109f3fa71be44d5c3701d73141d494510",
   "v8/tools/clang":
-    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "50fc8b6e785aa002218d67b78db871b21b1c9d71",
+    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "a8adb78c8eda9bddb2aa9c51f3fee60296de1ad4",
 }
 
 deps_os = {