[libc++][test] cleanup in formatter.h

[CaseyCarter]

Summary

• Silence warnings for unused parameters / variables
• There's no reason to output unexpected exceptions only for libc++

[Mordante]

I've been working on a more generic way for test validation, so I probably will change this code in the near future.
But the current version is an improvement, LGTM thanks!

Note the CI errors are unrelated.

libcxx/test/std/time/time.syn/formatter_tests.h

98

Nice catch, usually I have tests where I validate e.what() == expected which is libc++ specific. This one indeed is generic.

libcxx/test/std/time/time.syn/formatter_tests.h

try {
     assert(false);
   } catch (const std::format_error& e) {
 #  if defined(_LIBCPP_VERSION)
     if constexpr (std::same_as<CharT, char>)
       if (e.what() != what)
         std::cerr << "\nFormat string   " << fmt << "\nExpected exception " << what << "\nActual exception   "
                   << e.what() << '\n';
     assert(e.what() == what);
+#  else
+    (void)what;
+    (void)e;
 #  endif
     return;
   }
   assert(false);
 #endif
 }
 
 template <class CharT, class T>
 void check_invalid_type(const std::set<std::basic_string_view<CharT>>& valid_types,
                         std::string_view what,
                         std::basic_string<CharT> type,
                         const T& arg) {
   std::basic_string<CharT> fmt{STR("{:%") + type + STR("}")};
 
   if (valid_types.contains(std::basic_string_view<CharT>{type})) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
     try {
 #endif
       TEST_IGNORE_NODISCARD std::vformat(
           std::basic_string_view<CharT>{fmt}, std::make_format_args<format_context<CharT>>(arg));
 #ifndef TEST_HAS_NO_EXCEPTIONS
     } catch (const std::format_error& e) {
-#  if defined(_LIBCPP_VERSION)
+      (void)e;
       if constexpr (std::same_as<CharT, char>)
         std::cerr << "\nFormat string        " << fmt << "\nUnexpected exception " << e.what() << '\n';
-#  endif
       assert(false);
     }
 #endif
   } else {
     check_exception(what, std::basic_string_view<CharT>{fmt}, arg);
   }
 }