message: core: add warnings for Windows
  SITL autostart is not working on Windows, so we might as well warn.
  Also, it's good practice to use they keyword override.
diff: class SitlTest : public testing::Test
  {
  protected:
  - virtual void SetUp()
  + virtual void SetUp() override
  {
  #ifndef WINDOWS
  const int ret = system("./start_px4_sitl.sh");
  @@ -19,9 +19,11 @@ protected:
  }
  // We need to wait a bit until it's up and running.
  std::this_thread::sleep_for(std::chrono::seconds(3));
  +#else
  + dronecore::LogErr() << "Auto-starting SITL not supported on Windows.";
  #endif
  }
  - virtual void TearDown()
  + virtual void TearDown() override
  {
  #ifndef WINDOWS
  // Don't rush this either.
  @@ -31,6 +33,8 @@ protected:
  dronecore::LogErr() << "./stop_px4_sitl.sh failed, giving up.";
  abort();
  }
  +#else
  + dronecore::LogErr() << "Auto-starting SITL not supported on Windows.";
  #endif
  }
  };
  