[clang] p1099 using-enum feature macro & web page

This completes the series implementing p1099, by adding the feature
macro and updating the web page.

Differential Revision: https://reviews.llvm.org/D102242

clang/lib/Frontend/InitPreprocessor.cpp

@@ -594,7 +594,7 @@ static void InitializeCPlusPlusFeatureTestMacros(const LangOptions &LangOpts,
     Builder.defineMacro("__cpp_designated_initializers", "201707L");
     Builder.defineMacro("__cpp_impl_three_way_comparison", "201907L");
     //Builder.defineMacro("__cpp_modules", "201907L");
-    //Builder.defineMacro("__cpp_using_enum", "201907L");
+    Builder.defineMacro("__cpp_using_enum", "201907L");
   }
   // C++2b features.
   if (LangOpts.CPlusPlus2b)

clang/test/Lexer/cxx-features.cpp

@@ -98,8 +98,7 @@
 #error "wrong value for __cpp_modules"
 #endif
 
-#if check(using_enum, 0, 0, 0, 0, 0, 0)
-// FIXME: 201907 in C++20
+#if check(using_enum, 0, 0, 0, 0, 201907, 201907)
 #error "wrong value for __cpp_using_enum"
 #endif
 

clang/www/cxx_status.html

@@ -1205,7 +1205,7 @@ code. This issue is expected to be rectified soon.
     <tr>
       <td><tt>using enum</tt></td>
       <td><a href="https://wg21.link/p1099r5">P1099R5</a></td>
-      <td class="none" align="center">No</td>
+      <td class="unreleased" align="center">Clang 13</td>
     </tr>
     <tr>
       <td rowspan=2>Class template argument deduction for aggregates</td>