[libcxx] Mark do_open, do_get and do_close parameters unused when catopen is missing

[phosek]

Summary

When catopen is missing, do_open, do_get and do_close end up being
no-op, and as such their parameters will be unused which triggers a
warning when building with -Wunused-parameter.

[mclow.lists]

libcxx/include/locale

3565

Looking at this, I frowned. It seems like a lot of text just to remove a parameter name.

I went looking in the rest of libc++, and I found places in <unordered_map> where we say ((void)__p) and in <stdexcept> where we say ((void)__msg) rather than conditionally remove the parameter name.

This makes me think that a _LIBCPP_UNUSED_VAR macro might be useful; it would make it clear what we're trying to accomplish: #define _LIBCPP_UNUSED_VAR(x) ((void)(x))

[mclow.lists]

I like this much better now; making a note to myself to go back to <unordered_map> and <stdexcept> and use this there.

libcxx/include/locale

 };
 
 template <class _CharT>
 locale::id
 messages<_CharT>::id;
 
 template <class _CharT>
 typename messages<_CharT>::catalog
+#ifdef _LIBCPP_HAS_CATOPEN
 messages<_CharT>::do_open(const basic_string<char>& __nm, const locale&) const
+#else // !_LIBCPP_HAS_CATOPEN
+messages<_CharT>::do_open(const basic_string<char>&, const locale&) const
+#endif // _LIBCPP_HAS_CATOPEN
 {
 #ifdef _LIBCPP_HAS_CATOPEN
     catalog __cat = (catalog)catopen(__nm.c_str(), NL_CAT_LOCALE);
     if (__cat != -1)
         __cat = static_cast<catalog>((static_cast<size_t>(__cat) >> 1));
     return __cat;
 #else // !_LIBCPP_HAS_CATOPEN
     return -1;
 #endif // _LIBCPP_HAS_CATOPEN
 }
 
 template <class _CharT>
 typename messages<_CharT>::string_type
+#ifdef _LIBCPP_HAS_CATOPEN
 messages<_CharT>::do_get(catalog __c, int __set, int __msgid,
                          const string_type& __dflt) const
+#else // !_LIBCPP_HAS_CATOPEN
+messages<_CharT>::do_get(catalog, int, int, const string_type& __dflt) const
+#endif // _LIBCPP_HAS_CATOPEN
 {
 #ifdef _LIBCPP_HAS_CATOPEN
     string __ndflt;
     __narrow_to_utf8<sizeof(char_type)*__CHAR_BIT__>()(back_inserter(__ndflt),
                                                        __dflt.c_str(),
                                                        __dflt.c_str() + __dflt.size());
     if (__c != -1)
         __c <<= 1;
     nl_catd __cat = (nl_catd)__c;
     char* __n = catgets(__cat, __set, __msgid, __ndflt.c_str());
     string_type __w;
     __widen_from_utf8<sizeof(char_type)*__CHAR_BIT__>()(back_inserter(__w),
                                                         __n, __n + strlen(__n));
     return __w;
 #else // !_LIBCPP_HAS_CATOPEN
     return __dflt;
 #endif // _LIBCPP_HAS_CATOPEN
 }
 
 template <class _CharT>
 void
+#ifdef _LIBCPP_HAS_CATOPEN
 messages<_CharT>::do_close(catalog __c) const
+#else // !_LIBCPP_HAS_CATOPEN
+messages<_CharT>::do_close(catalog) const
+#endif // _LIBCPP_HAS_CATOPEN
 {
 #ifdef _LIBCPP_HAS_CATOPEN
     if (__c != -1)
         __c <<= 1;
     nl_catd __cat = (nl_catd)__c;
     catclose(__cat);
 #endif // _LIBCPP_HAS_CATOPEN
 }