Guard system-instrumentation with V8_OS_WIN instead of V8_TARGET_OS_WIN. Re-enable ENABLE_SYSTEM_INSTRUMENTATION

Bug: v8:11043, chromium:1196278
Change-Id: I3c3ab07de909ad5b58dd9a99740ff5f59ab8165f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2809530Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Sara Tang <sartang@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#73821}