These are the changes Cobalt currently has in V8's cpu related code.
- Add missing Starboard CPU code
- Replace some V8_OS_WIN with V8_TARGET_OS_WIN, they are found when
  cross-compiling for Linux platforms on Windows

Bug: v8:10927
Change-Id: Id63ae8614cbe6fe0eb53df89060c8ca2c9969ef4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2963803
Commit-Queue: John Xu <johnx@google.com>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75318}