[build] Update V8 DEPS

Rolling v8/tools/clang to
b6f620b311665e2d96d0921833f54295b9bbf925

Porting parts of https://codereview.chromium.org/1917853002

BUG=604993
LOG=n
TBR=thakis@chromium.org, jochen@chromium.org

Review URL: https://codereview.chromium.org/1923473002

Cr-Commit-Position: refs/heads/master@{#35782}

DEPS

@@ -29,7 +29,7 @@ deps = {
   "v8/test/test262/data":
     Var("git_url") + "/external/github.com/tc39/test262.git" + "@" + "57d3e2216fa86ad63b6c0a54914ba9dcbff96003",
   "v8/tools/clang":
-    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "db76f9f1d1ed7f4c4db1bf10f530506614375db3",
+    Var("git_url") + "/chromium/src/tools/clang.git" + "@" + "b6f620b311665e2d96d0921833f54295b9bbf925",
 }
 
 deps_os = {

build/standalone.gypi

@@ -389,7 +389,10 @@
   'target_defaults': {
     'variables': {
       'v8_code%': '<(v8_code)',
-      'clang_warning_flags': [],
+      'clang_warning_flags': [
+        # TODO(thakis): https://crbug.com/604888
+        '-Wno-undefined-var-template',
+      ],
       'conditions':[
         ['OS=="android"', {
           'host_os%': '<(host_os)',