Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/7571a8a..8b49e99

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

Change-Id: I23ffca10b9188f67adf5fd9436f71974f9db85e4
Reviewed-on: https://chromium-review.googlesource.com/505637Reviewed-by: v8 autoroll <v8-autoroll@chromium.org>
Commit-Queue: v8 autoroll <v8-autoroll@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45357}

DEPS

@@ -8,7 +8,7 @@ vars = {
 
 deps = {
   "v8/build":
-    Var("chromium_url") + "/chromium/src/build.git" + "@" + "7571a8a7310ab694f4f3fb4e398d571d830b0fb8",
+    Var("chromium_url") + "/chromium/src/build.git" + "@" + "8b49e999ee2c152abf53d7a923eaca518f3089ed",
   "v8/tools/gyp":
     Var("chromium_url") + "/external/gyp.git" + "@" + "eb296f67da078ec01f5e3a9ea9cdc6d26d680161",
   "v8/third_party/icu":