[gcc r16-4377] libstdc++: Update Autoconf manual link

[Gerald Pfeifer]

https://gcc.gnu.org/g:c1a8b4fa50707ce1e5dbf5d963d8868f88caef67

commit r16-4377-gc1a8b4fa50707ce1e5dbf5d963d8868f88caef67
Author: Gerald Pfeifer <gerald@pfeifer.com>
Date:   Sat Oct 11 12:18:56 2025 +0200

    libstdc++: Update Autoconf manual link
    
    libstdc++-v3:
            * doc/xml/manual/build_hacking.xml: Update Autoconf manual link.
            * doc/html/manual/appendix_porting.html: Regenerate.

Diff:
---
 libstdc++-v3/doc/html/manual/appendix_porting.html | 2 +-
 libstdc++-v3/doc/xml/manual/build_hacking.xml      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/doc/html/manual/appendix_porting.html b/libstdc++-v3/doc/html/manual/appendix_porting.html
index 7b63613a5513..00677461ea12 100644
--- a/libstdc++-v3/doc/html/manual/appendix_porting.html
+++ b/libstdc++-v3/doc/html/manual/appendix_porting.html
@@ -237,7 +237,7 @@ in the build directory starts the build process. The <code class="literal">all</
    </p><p>
      If you're wondering what that line noise in the last example was,
      that's how you embed autoconf special characters in output text.
-     They're called <a class="link" href="http://www.gnu.org/software/autoconf/manual/autoconf.html#Quadrigraphs" target="_top"><span class="emphasis"><em>quadrigraphs</em></span></a>
+     They're called <a class="link" href="https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/" target="_top"><span class="emphasis"><em>quadrigraphs</em></span></a>
      and you should use them whenever necessary.
  </p></li><li class="listitem"><p><code class="literal">HELP-STRING</code> is what you think it is.  Do not include the
    "default" text like we used to do; it will be done for you by
diff --git a/libstdc++-v3/doc/xml/manual/build_hacking.xml b/libstdc++-v3/doc/xml/manual/build_hacking.xml
index 4c044d97cab7..47d9db5e7ba0 100644
--- a/libstdc++-v3/doc/xml/manual/build_hacking.xml
+++ b/libstdc++-v3/doc/xml/manual/build_hacking.xml
@@ -350,7 +350,7 @@ in the build directory starts the build process. The <literal>all</literal> targ
    <para>
      If you're wondering what that line noise in the last example was,
      that's how you embed autoconf special characters in output text.
-     They're called <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.gnu.org/software/autoconf/manual/autoconf.html#Quadrigraphs"><emphasis>quadrigraphs</emphasis></link>
+     They're called <link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/"><emphasis>quadrigraphs</emphasis></link>
      and you should use them whenever necessary.
  </para>
  </listitem>