Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/4161431..9d6666d

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

Change-Id: I3bddd9d99ea1840cce06dcb2c5b2bed33d2e7a7b
Reviewed-on: https://chromium-review.googlesource.com/527576Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45788}

DEPS

@@ -8,7 +8,7 @@ vars = {
 
 deps = {
   "v8/build":
-    Var("chromium_url") + "/chromium/src/build.git" + "@" + "4161431eb4031f1a8d9b4f488d1cafa5bd5cf5de",
+    Var("chromium_url") + "/chromium/src/build.git" + "@" + "9d6666d50f168886cae4990af7a44d8cd1fa1a9d",
   "v8/tools/gyp":
     Var("chromium_url") + "/external/gyp.git" + "@" + "eb296f67da078ec01f5e3a9ea9cdc6d26d680161",
   "v8/third_party/icu":