docs: note change in minimum GCC version to 4.1.0

Signed-off-by: Timothy Arceri <t_arceri@yahoo.com.au>
Reviewed-by: Matt Turner <mattst88@gmail.com>

docs/relnotes/10.5.0.html

@@ -59,6 +59,7 @@ TBD.
 <h2>Changes</h2>
 
 <ul>
+<li>Removed support for GCC versions earlier than 4.1.0.</li>
 </ul>
 
 </div>