[committed][wwwdocs] Add notes about and header dependencies

[Jonathan Wakely via Gcc-patches]

I backported a change to the <string> header which meant it no longer
includes <pthread.h>, which broke some (incorrect) packages. This
updates the GCC 12 docs to mention it.

Pushed to wwwdocs.

-- >8 --

Also fix missing closing tag for <p>.
---
 htdocs/gcc-12/porting_to.html | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/htdocs/gcc-12/porting_to.html b/htdocs/gcc-12/porting_to.html
index 079bda30..3badb0cc 100644
--- a/htdocs/gcc-12/porting_to.html
+++ b/htdocs/gcc-12/porting_to.html
@@ -82,6 +82,12 @@ be included explicitly when compiled with GCC 12:
 <li> <code>&lt;atomic&gt;</code>
   (for <code>std::atomic</code>)
 </li>
+<li> <code>&lt;ctime&gt;</code>
+  (for <code>std::time</code>, <code>std::mktime</code> etc.)
+</li>
+<li> <code>&lt;pthread.h&gt;</code>
+  (for <code>pthread_create</code>, <code>pthread_mutex_t</code> etc.)
+</li>
 </ul>
 
 <h3 id="cxx-deprecations">C++ Standard Library deprecations</h3>
@@ -109,6 +115,8 @@ GCC 12 now uses <code>OPERATION</code> as the name of the 
function to
 the <code>CO_REDUCE</code> intrinsic for the pairwise reduction, thus
 conforming to the Fortran 2018 standard.  Previous versions
 used <code>OPERATOR</code>, which conformed to TS 18508.
+</p>
+
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 <h2 id="links">Links</h2>
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-- 
2.36.1