[wwwdocs] Document libstdc++ freestanding changes in gcc-13

[wwwdocs] Document libstdc++ freestanding changes in gcc-13

[Jonathan Wakely]

Pushed to wwwdocs (better late than never).

-- >8 --

---
 htdocs/gcc-13/changes.html | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/htdocs/gcc-13/changes.html b/htdocs/gcc-13/changes.html
index bd022ed2..39414e18 100644
--- a/htdocs/gcc-13/changes.html
+++ b/htdocs/gcc-13/changes.html
@@ -412,6 +412,20 @@ You may also want to check out our
   <li>Support for the <code>&lt;experimental/synchronized_value&gt;</code>
       header from v2 of the Concurrency Technical Specification.
   </li>
+  <li>Support for many previously unavailable features in freestanding mode,
+      thanks to Arsen Arsenović. For example, <code>std::tuple</code> is
+      now available for freestanding compilation. The freestanding subset
+      contains all the components made freestanding by
+      <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p1642r11.html">P1642</a>,
+      but libstdc++ adds more components to the freestanding subset,
+      such as <code>std::array</code> and <code>std::string_view</code>.
+      Additionally, libstdc++ now respects the <code>-ffreestanding</code>
+      compiler option and so it is not necessary to build a separate
+      freestanding installation of libstdc++.  Compiling with
+      <code>-ffreestanding</code> will restrict the available features to
+      the freestanding subset, even if libstdc++ was built as a full, hosted
+      implementation.
+  </li>
 </ul>
 
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