[committed 3/4] libstdc++: Update C++23 status docs

[Jonathan Wakely]

This documents the partial support for P2231 in the gcc-11 branch,
pushed to that branch.
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commit 5d418194ccb39346d2ad022c5b143fe00b2340ac
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon May 16 15:33:06 2022

    libstdc++: Document support for constexpr optional (P2231R1)
    
    The changes for std::variant are not on the gcc-11 branch though.
    
    libstdc++-v3/ChangeLog:
    
            * doc/xml/manual/status_cxx2023.xml: Update status.
            * doc/html/manual/status.html: Regenerate.

diff --git a/libstdc++-v3/doc/xml/manual/status_cxx2023.xml b/libstdc++-v3/doc/xml/manual/status_cxx2023.xml
index f1244da9dc8..75f31f55aa9 100644
--- a/libstdc++-v3/doc/xml/manual/status_cxx2023.xml
+++ b/libstdc++-v3/doc/xml/manual/status_cxx2023.xml
@@ -158,6 +158,23 @@ or any notes about the implementation.
       <entry> <code>__cpp_lib_to_underlying >= 202102L</code> </entry>
     </row>
 
+    <row>
+      <?dbhtml bgcolor="#B0B0B0" ?>
+      <entry> Missing constexpr in std::optional and std::variant </entry>
+      <entry>
+        <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2231r1.html">
+        P2231R1
+        </link>
+      </entry>
+      <entry align="center"> 11.3 (<code>optional</code> only) </entry>
+      <entry>
+	<informaltable colsep="0" rowsep="0" rowheader="norowheader" frame="none"><tgroup cols="1"><tbody>
+        <row><entry> <code>__cpp_lib_constexpr_optional >= 202106L</code> </entry></row>
+        <row><entry> <code>__cpp_lib_variant >= 202106L</code> </entry></row>
+        </tbody></tgroup></informaltable>
+      </entry>
+    </row>
+
     <row>
       <entry namest="c1" nameend="c4" align="left">
         <emphasis role="bold">Strings and text</emphasis>