Avoid -Wduplicated-cond warnings in gdb/python

I tried building gdb with -Wduplicated-cond.  This patch fixes the
simpler issue that was found.

In Python 3, "int" and "long" are synonyms, so code like:

      else if (PyLong_Check (obj))
...
      else if (PyInt_Check (obj))

.... will trigger this warning.  The fix is to conditionalize the
PyInt_Check branches on Python 2.

Tested by rebuilding, with both version of Python, on x86-64 Fedora 24.

2016-09-20  Tom Tromey  <tom@tromey.com>

	* python/py-value.c (convert_value_from_python): Make PyInt_Check
	conditional on Python 2.
	* python/py-arch.c (archpy_disassemble): Make PyInt_Check
	conditional on Python 2.

gdb/python/py-arch.c

@@ -141,10 +141,12 @@ archpy_disassemble (PyObject *self, PyObject *args, PyObject *kw)
 	 conversion process.  */
       if (PyLong_Check (end_obj))
         end = PyLong_AsUnsignedLongLong (end_obj);
+#if PY_MAJOR_VERSION == 2
       else if (PyInt_Check (end_obj))
         /* If the end_pc value is specified without a trailing 'L', end_obj will
            be an integer and not a long integer.  */
         end = PyInt_AsLong (end_obj);
+#endif
       else
         {
           Py_DECREF (end_obj);