AP_HAL_SITL: fix compile error for Windows/Cygwin builds

termios2 not available on cygwin. This needs a re-think for cygwin. For now let's just hide it by letting it be declared empty by the virtual and totally bypass it in the cygwin build.

libraries/AP_HAL_SITL/UARTDriver.h

@@ -61,9 +61,9 @@ public:
 
     enum flow_control get_flow_control(void) { return FLOW_CONTROL_ENABLE; }
 
-    virtual bool set_speed(int speed);
-    virtual void configure_parity(uint8_t v);
-    virtual void set_stop_bits(int n);
+    virtual bool set_speed(int speed) { return true; }
+    virtual void configure_parity(uint8_t v) { }
+    virtual void set_stop_bits(int n) { }
     bool set_unbuffered_writes(bool on);
 
     void _timer_tick(void);

libraries/AP_HAL_SITL/UART_utils.cpp

@@ -15,7 +15,7 @@
  * with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 #include <AP_HAL/AP_HAL.h>
-#if CONFIG_HAL_BOARD == HAL_BOARD_SITL
+#if CONFIG_HAL_BOARD == HAL_BOARD_SITL && !defined(__CYGWIN__)
 
 #include "UARTDriver.h"