[PATCH] wwwdocs: Document several further C++23 changes

[Jakub Jelinek <jakub@redhat.com>]

Hi!

Tobias mentioned on IRC that assume attribute wasn't mentioned in
changes.html.  The P1774R8 entry was missing for C++, so I went through
projects/cxx-status.html#cxx23 and filled in all the missing papers
which have been implemented newly in GCC 13, plus a small note for C family
about assume attribute.

Ok for wwwdocs?

diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index 410594ae..839b73d0 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -182,6 +182,10 @@ a work-in-progress.</p>
     <a href="https://gcc.gnu.org/onlinedocs/gcc/Static-Analyzer-Options.html"><code>-fanalyzer</code></a>
     to detect misuses of file descriptors.
   </li>
+  <li>A new statement attribute for C++23 <a href="https://wg21.link/p1774r8">P1774R8</a> Portable
+      assumptions support also in C or older C++:
+    <a href="https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#index-assume-statement-attribute"><code>__attribute__((assume(EXPR)));</code>
+  </li>
 </ul>
 
 <h3 id="c">C</h3>
@@ -290,6 +294,29 @@ a work-in-progress.</p>
 	Operator You Are Looking For
 	(<a href="https://gcc.gnu.org/PR106644">PR106644</a>)
       </li>
+      <li> <a href="https://wg21.link/p2362r3">P2362R3</a>, Remove non-encodable
+          wide character literals and multicharacter wide character literals
+	(<a href="https://gcc.gnu.org/PR106647">PR106647</a>)
+      </li>
+      <li> <a href="https://wg21.link/p2448r2">P2448R2</a>, Relaxing some
+          constexpr restrictions
+	(<a href="https://gcc.gnu.org/PR106649">PR106649</a>)
+      </li>
+      <li> <a href="https://wg21.link/p1467r9">P1467R9</a>, Extended
+          floating-point types and standard names
+	(<a href="https://gcc.gnu.org/PR106652">PR106652</a>)
+      </li>
+      <li> <a href="https://wg21.link/p1774r8">P1774R8</a>, Portable
+          assumptions
+	(<a href="https://gcc.gnu.org/PR106654">PR106654</a>)
+      </li>
+      <li> <a href="https://wg21.link/p2295r6">P2295R6</a>, Support for
+          UTF-8 as a portable source file encoding
+	(<a href="https://gcc.gnu.org/PR106655">PR106655</a>)
+      </li>
+      <li> <a href="https://wg21.link/p2589r1">P2589R1</a>, static operator[]
+	(<a href="https://gcc.gnu.org/PR107684">PR107684</a>)
+      </li>
     </ul>
   </li>
   <li>New warnings:

	Jakub