Issue with mbed compile for GCC_ARM tool resolved

Functions 'serial_break_set' & 'serial_break_clear' wrongly removed during 'SERIAL_FC disabled, critical section API Updation' commit.
Due to this 'mbed compile' command for GCC_ARM tool fails to compile.

targets/TARGET_TOSHIBA/TARGET_TMPM066/serial_api.c

@@ -239,3 +239,11 @@ void serial_pinout_tx(PinName tx)
 {
     pinmap_pinout(tx, PinMap_UART_TX);
 }
+
+void serial_break_set(serial_t *obj)
+{
+}
+
+void serial_break_clear(serial_t *obj)
+{
+}