[wwwdocs] Document new libstdc++ header dependency changes

[Jonathan Wakely]

Pushed to wwwdocs.

-- >8 --

---
 htdocs/gcc-13/porting_to.html | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/htdocs/gcc-13/porting_to.html b/htdocs/gcc-13/porting_to.html
index 7a67c0b0..9a9a3147 100644
--- a/htdocs/gcc-13/porting_to.html
+++ b/htdocs/gcc-13/porting_to.html
@@ -34,12 +34,26 @@ including the right headers will no longer compile.
 </p>
 <p>
 The following headers are used less widely in libstdc++ and may need to
-be included explicitly when compiled with GCC 13:
+be included explicitly when compiling with GCC 13:
 </p>
 <ul>
+<li> <code><string></code>
+  (for <code>std::string</code>, <code>std::to_string</code>,
+  <code>std::stoi</code> etc.)
+</li>
+<li> <code><system_error></code>
+  (for <code>std::error_code</code>, <code>std::error_category</code>,
+  <code>std::system_error</code>).
+</li>
 <li> <code><cstdint></code>
   (for <code>std::int8_t</code>, <code>std::int32_t</code> etc.)
 </li>
+<li> <code><cstdio></code>
+  (for <code>std::printf</code>, <code>std::fopen</code> etc.)
+</li>
+<li> <code><cstdlib></code>
+  (for <code>std::strtol</code>, <code>std::malloc</code> etc.)
+</li>
 </ul>
 
 <h3 id="P2266">Implicit move rules change</h3>
-- 
2.39.0