Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/568bd76..7a702b2

TBR=machenbach@chromium.org,tmrts@chromium.org,v8-waterfall-sheriff@grotations.appspotmail.com

Change-Id: I4a6400cfa7e2b7ae8737fd263ed01b877d1ead45
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2661901Reviewed-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@{#72449}

DEPS

@@ -88,7 +88,7 @@ vars = {
 
 deps = {
   'build':
-    Var('chromium_url') + '/chromium/src/build.git' + '@' + '568bd7641c0926ac004ddd58c6895b48ac93645f',
+    Var('chromium_url') + '/chromium/src/build.git' + '@' + '7a702b2a7548484b2bea2b869fe85972c39a76bc',
   'third_party/depot_tools':
     Var('chromium_url') + '/chromium/tools/depot_tools.git' + '@' + 'cb07c525c00132fc8cb52cdff78e1078c280a4a1',
   'third_party/icu':