Mention GCC's optional dependencies. Fixes #2521.

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@9177 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

appendices/dependencies.xml

@@ -609,7 +609,9 @@
         <segtitle>&external;</segtitle>
 
         <seglistitem>
-          <seg>GNAT</seg>
+          <seg><ulink url="http://gcc.gnu.org/wiki/Graphite">CLooG-PPL</ulink>,
+               <ulink url="http://gcc.gnu.org/wiki/GNAT">GNAT</ulink> and
+               <ulink url="http://gcc.gnu.org/wiki/Graphite">PPL</ulink></seg>
         </seglistitem>
       </segmentedlist>