Update V8 DEPS.

Rolling v8/build: https://chromium.googlesource.com/chromium/src/build/+log/b3c270e..2f9b06d

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

Change-Id: I5045137ed959ea43bf1262b9f99a42aa66644e7c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2608123Reviewed-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@{#71898}

DEPS

@@ -88,7 +88,7 @@ vars = {
 
 deps = {
   'build':
-    Var('chromium_url') + '/chromium/src/build.git' + '@' + 'b3c270e43c03ad0b1cde3f34a88ba183fc073b10',
+    Var('chromium_url') + '/chromium/src/build.git' + '@' + '2f9b06d9efc00157e66edca575d74712164a8148',
   'third_party/depot_tools':
     Var('chromium_url') + '/chromium/tools/depot_tools.git' + '@' + '364205c70ed16c00802b1c264e88d8e03a0b37ae',
   'third_party/icu':