toolchaintechnotes: reword the reason "cc-lfs not usable on pc"

The problem is not "gcc building system doesn't know cc-lfs can run on
pc", but "cc-lfs really cannot run on pc".

Let's stop anyone from thinking about "why not just tell the gcc
building system the fact".

part3intro/toolchaintechnotes.xml

@@ -257,11 +257,28 @@
     paragraph is that cc1 is unable to build a fully functional libstdc++, but
     this is the only compiler available for building the C/C++ libraries
     during stage 2. Of course, the compiler built by stage 2, cc-lfs,
-    would be able to build those libraries, but (1) the build system of
-    gcc does not know cc-lfs can run on pc, and (2) using cc-lfs on pc
-    would create a risk of linking to the pc libraries, since cc-lfs is a native
-    compiler. So we have to re-build libstdc++ later as a part of
-    gcc stage 2.</para>
+    would be able to build those libraries, but:</para>
+
+    <itemizedlist>
+      <listitem>
+        <para>
+          Generally cc-lfs cannot run on pc (the host distro).  Despite the
+          triplets of pc and lfs are compatible to each other, an executable
+          for lfs will depend on glibc-&glibc-version; while the host distro
+          may utilizes a different libc implementation (for example, musl) or
+          a previous release of glibc (for example, glibc-2.13).
+        </para>
+      </listitem>
+      <listitem>
+        <para>
+          Even if cc-lfs happens to run on pc, using it on pc would create
+          a risk of linking to the pc libraries, since cc-lfs is a native
+          compiler.
+        </para>
+      </listitem>
+    </itemizedlist>
+
+    <para>So we have to re-build libstdc++ later as a part of gcc stage 2.</para>
 
     <para>In &ch-final; (or <quote>stage 3</quote>), all the packages needed for
     the LFS system are built. Even if a package has already been installed into