Update description/rationale for Libstdc++ in Chapter 5

git-svn-id: http://svn.linuxfromscratch.org/LFS/trunk/BOOK@11424 4aa44e1e-78dd-0310-a6d2-fbcd4c07a689

chapter05/gcc-pass1.xml

@@ -5,7 +5,7 @@
   %general-entities;
 ]>
 
-<sect1 id="ch-tools-gcc-pass1" role="wrap">
+<sect1 id="ch-tools-gcc-pass1" role="wrap" xreflabel="gcc-pass1">
   <?dbhtml filename="gcc-pass1.html"?>
 
   <sect1info condition="script">

chapter05/libstdc++.xml

@@ -14,7 +14,7 @@
     <address>&gcc-url;</address>
   </sect1info>
 
-  <title>Libstdc++-&gcc-version;</title>
+  <title>Libstdc++ from GCC-&gcc-version;</title>
 
   <indexterm zone="ch-tools-libstdcpp">
     <primary sortas="a-GCC">GCC</primary>
@@ -24,8 +24,12 @@
   <sect2 role="package">
     <title/>
 
-    <para>Libstdc++ is the standard C++ library. It is needed for the correct
-    operation of the g++ compiler.</para>
+    <para>Libstdc++ is the standard C++ library. It is needed 
+    to compile C++ code
+    (part of GCC is written in C++), but we had to defer its installation
+    when we built <xref linkend="ch-tools-gcc-pass1"/>
+    because it depends on glibc, which was not yet available in /tools.
+    </para>
 
     <segmentedlist>
       <segtitle>&buildtime;</segtitle>