Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/e270920..9578c43

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

Change-Id: I67c5cb1f4f781605098e106289061d4f4e449236
Reviewed-on: https://chromium-review.googlesource.com/c/1279935
Commit-Queue: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Reviewed-by: v8-ci-autoroll-builder <v8-ci-autoroll-builder@chops-service-accounts.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#56620}

DEPS

@@ -13,7 +13,7 @@ vars = {
 
 deps = {
   'v8/build':
-    Var('chromium_url') + '/chromium/src/build.git' + '@' + 'e270920c75ea1334f5376c2a22e7a4f65abb2e80',
+    Var('chromium_url') + '/chromium/src/build.git' + '@' + '9578c43c3d2e17cbd5fee58d0ee38958f67b0334',
   'v8/third_party/depot_tools':
     Var('chromium_url') + '/chromium/tools/depot_tools.git' + '@' + 'dd78844442fef7e3613f6896dbe325cffb495a66',
   'v8/third_party/icu':