Fix some harmless unused parameter warnings.

These warnings only happen in specific builds (when HAVE_LANGINFO_H and
wxUSE_DISPLAY are undefined/off).

See #11817.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63720 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/intl.cpp

@@ -3097,6 +3097,8 @@ wxString GetDateFormatFromLangInfo(wxLocaleInfo index)
 
     return fmtDateOnly;
 #else // !HAVE_LANGINFO_H
+    wxUnusedVar(index);
+
     // no fallback, let the application deal with unavailability of
     // nl_langinfo() itself as there is no good way for us to do it (well, we
     // could try to reverse engineer the format from strftime() output but this