Add unistd.h in libs/thirdParty/qserialport/src/posix/qserialportnative_posix.cpp.

Without this change, the program can not be built on Linux.

libs/thirdParty/qserialport/src/posix/qserialportnative_posix.cpp

@@ -28,6 +28,7 @@
 #include <QSocketNotifier>
 #include "qserialportnative.h"
 #include "termioshelper.h"
+#include <unistd.h>
 
 namespace {
   const int kMinReadTimeout = 100;