exit: Add changelog and warning about updated exit code behaviour since PHP 8.4.0 (#5579)

* Add changelog and warning about updated exit code bahaviour since PHP 8.4.0

Co-authored-by: Louis-Arnaud <la.catoire@gmail.com>

Author: PrinsFrank

reference/funchand/functions/register-shutdown-function.xml

@@ -24,6 +24,14 @@
    function, processing will stop completely and no other registered
    shutdown functions will be called.
   </para>
+  <caution>
+   <simpara>
+    Since PHP 8.4.0, a parameterless <function>exit</function> call within a
+    registered shutdown function resets the exit code to <literal>0</literal>.
+    Calling <function>exit</function> with an explicit status overwrites the
+    previous exit code in all versions.
+   </simpara>
+  </caution>
   <para>
    Shutdown functions may also call <function>register_shutdown_function</function>
    themselves to add a shutdown function to the end of the queue.

reference/misc/functions/exit.xml

@@ -109,6 +109,16 @@
        <link linkend="functions.variable-functions">variable functions</link>.
       </entry>
      </row>
+     <row>
+      <entry>8.4.0</entry>
+      <entry>
+       A parameterless <function>exit</function> called within
+       <link linkend="function.register-shutdown-function">shutdown functions</link>
+       or <link linkend="language.oop5.decon.destructor">object destructors</link>
+       now resets the exit code to <literal>0</literal>; previously the exit code
+       set by an earlier <function>exit</function> call was kept.
+      </entry>
+     </row>
     </tbody>
    </tgroup>
   </informaltable>