diffutils: Use an easier work around for the strcasecmp check and improve the explanation

chapter06/diffutils.xml

@@ -43,21 +43,40 @@
   <sect2 role="installation">
     <title>Installation of Diffutils</title>
 
-    <para>When Diffutils is being configured, it checks to see if it is
-    being cross compiled. If it is, configuration fails. Since we are
-    cross compiling, comment out the specific lines that perform that
-    test now:</para>
-
-    <screen><userinput remap="pre">sed -e '46252,+3 s/^/#/' \
-    -e '46596,+3 s/^/#/' \
-    -i configure</userinput></screen>
-
     <para>Prepare Diffutils for compilation:</para>
 
     <screen><userinput remap="configure">./configure --prefix=/usr   \
             --host=$LFS_TGT \
+            gl_cv_func_strcasecmp_works=y \
             --build=$(./build-aux/config.guess)</userinput></screen>
 
+    <variablelist>
+      <title>The meaning of the configure options:</title>
+
+      <varlistentry>
+        <!-- https://git.savannah.gnu.org/cgit/gnulib.git/commit/?id=d9083a4cc638cf9c7dfc3cc534a7c6b4debf50ab -->
+        <term><parameter>gl_cv_func_strcasecmp_works=y</parameter></term>
+        <listitem>
+          <para>This option specify the result of a check for the
+          <function>strcasecmp</function>.  The check requires running a
+          compiled C program, and this is impossible during
+          cross-compilation because in general a cross-compiled program
+          cannot run on the host distro.  Normally for such a check the
+          <command>configure</command> script would use a fall-back value
+          for cross-compilation, but the fall-back value for this check is
+          absent and the <command>configure</command> script would have no
+          value to use and error out.  The upstream has already fixed the
+          issue, but to apply the fix we'd need to run
+          <command>autoconf</command> that the host distro may lack.  So
+          we just specify the check result (<literal>y</literal> as we know
+          the <function>strcasecmp</function> function in
+          Glibc-&glibc-version; works fine) instead, then
+          <command>configure</command> will just use the specified value and
+          skip the check.</para>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+
     <para>Compile the package:</para>
 
 <screen><userinput remap="make">make</userinput></screen>