The Chromium 64-bit Windows build uses "Debug_x64" and "Release_x64"
as configs for some reason, so put v8's build config settings there
too.

Reduces e.g. the runtime of CrSettingsBrowserTest.CrSettingsTest from
25s to 12s on my z840 in a 64-bit Chromium debug build
(while also turning on handle zapping).

BUG=chromium:586511
LOG=n

Review URL: https://codereview.chromium.org/1852913002

Cr-Commit-Position: refs/heads/master@{#35224}