libstdc++: Move "free books" list from fsf.org to gnu.org

* doc/xml/manual/appendix_free.xml: Move "free books" list from
	fsf.org to gnu.org.
	* doc/html/manual/appendix_free.html: Regenerate.

libstdc++-v3/ChangeLog

@@ -1,3 +1,9 @@
+2020-04-01  Gerald Pfeifer  <gerald@pfeifer.com>
+
+	* doc/xml/manual/appendix_free.xml: Move "free books" list from
+	fsf.org to gnu.org.
+	* doc/html/manual/appendix_free.html: Regenerate.
+
 2020-03-31  Ville Voutilainen  <ville.voutilainen@gmail.com>
 
 	Library-side tests for parenthesized aggregate init

libstdc++-v3/doc/html/manual/appendix_free.html

@@ -116,7 +116,7 @@ manuals instead of proprietary ones.  One way you can help this is to
 check the distribution terms of a manual before you buy it, and
 prefer copylefted manuals to non-copylefted ones.
 </p><p>
-[Note: We now maintain a <a class="link" href="https://www.fsf.org/licensing/doc/other-free-books.html" target="_top">web page
+[Note: We now maintain a <a class="link" href="https://www.gnu.org/doc/other-free-books.html" target="_top">web page
 that lists free books available from other publishers</a>].
 </p><p>Copyright © 2004, 2005, 2006, 2007 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA</p><p>Verbatim copying and distribution of this entire article are
 permitted worldwide, without royalty, in any medium, provided this

libstdc++-v3/doc/xml/manual/appendix_free.xml

@@ -159,7 +159,7 @@ check the distribution terms of a manual before you buy it, and
 prefer copylefted manuals to non-copylefted ones.
 </para>
 <para>
-[Note: We now maintain a <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.fsf.org/licensing/doc/other-free-books.html">web page
+[Note: We now maintain a <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.gnu.org/doc/other-free-books.html">web page
 that lists free books available from other publishers</link>].
 </para>