Fix windows build error renaming stdout ivar

This fixes a build error on Windows by renaming the 'stdout' variable to
`sys_stdout' to avoid conflicts with system headers.

(cherry picked from commit commontk/PythonQt@5487c61)

Author: jcfr

src/PythonQt.cpp

@@ -1913,10 +1913,10 @@ bool PythonQt::redirectStdOutCallbackEnabled() const
   PythonQtObjectPtr pythonqt_stdout;
   pythonqt_stdout.setNewRef(PyObject_GetAttrString(sys.object(), "pythonqt_stdout"));
 
-  PythonQtObjectPtr stdout;
-  stdout.setNewRef(PyObject_GetAttrString(sys.object(), "stdout"));
+  PythonQtObjectPtr sys_stdout;
+  sys_stdout.setNewRef(PyObject_GetAttrString(sys.object(), "stdout"));
 
-  return PyObject_RichCompareBool(pythonqt_stdout.object(), stdout.object(), Py_EQ);
+  return PyObject_RichCompareBool(pythonqt_stdout.object(), sys_stdout.object(), Py_EQ);
 }
 
 void PythonQt::setRedirectStdOutCallbackEnabled(bool enabled)