Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/7f37dc1..70cbac6

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

Change-Id: I977ef05a0473602d831afd15de9a298bff9fb0de
Reviewed-on: https://chromium-review.googlesource.com/c/1390931Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Commit-Queue: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#58483}

DEPS

@@ -16,7 +16,7 @@ vars = {
 
 deps = {
   'v8/build':
-    Var('chromium_url') + '/chromium/src/build.git' + '@' + '7f37dc1237731e878be79820889691602c9ffc7b',
+    Var('chromium_url') + '/chromium/src/build.git' + '@' + '70cbac61b0ec2fa1215032eec02d819116ffd3a2',
   'v8/third_party/depot_tools':
     Var('chromium_url') + '/chromium/tools/depot_tools.git' + '@' + 'db0055dc786a71fe81e720bad2b1acb0e133a291',
   'v8/third_party/icu':