Add SERIAL_PORT_USBVIRTUAL and SerialUSB macros

This is needed to ensure compatibility with YunShield sketches

asas

Author: facchinm

variants/arduino_101/variant.h

@@ -202,10 +202,13 @@ void CDCSerial_bytes_sent(uint32_t num);
 // SERIAL_PORT_HARDWARE_OPEN  Hardware serial ports which are open for use.  Their RX & TX
 //                            pins are NOT connected to anything by default.
 #define SERIAL_PORT_MONITOR         Serial
+#define SERIAL_PORT_USBVIRTUAL      Serial
 #define SERIAL_PORT_HARDWARE_OPEN   Serial1
 #define SERIAL_PORT_HARDWARE        Serial1
 #define SERIAL_PORT_HARDWARE1       Serial1
 
+#define SerialUSB   SERIAL_PORT_USBVIRTUAL
+
 extern uint32_t sizeof_g_APinDescription;
 
 #endif /* _VARIANT_ARDUINO_101_X_ */