made operator definition dependent on sizeof(int), not __UNIX__

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@1071 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/string.h

@@ -303,9 +303,8 @@ public:
     char& Last()
       { wxASSERT( !IsEmpty() ); CopyBeforeWrite(); return m_pchData[Len()-1]; }
 
-    // Alternatively, we could uncomment one of them for 64bit platforms
-    // by using #if SIZEOF_INT > 32
-#ifdef __UNIX__
+    // on 64bit systems, this gives overload problems:
+#if SIZEOF_INT <= 32
     /// operator version of GetChar
     char  operator[](size_t n) const
       { ASSERT_VALID_INDEX( n ); return m_pchData[n]; }