patch 9.0.1823: Autoconf 2.69 too old

Problem:  Autoconf 2.69 too old
Solution: Migrate to Autoconf 2.71

Autoconf 2.69 is almost 10 years old.  And 2.71 is also a few years old
as well.  Should be pretty well tested by now.  It brings a lot of
improvements and there seems to be an ongoing work on autoconf 2.72
already.

This change just addresses two minor changes `autoupdate` suggested, and
then `src/auto/configure` is regenerated by running

  cd src
  make AUTOCONF=autoconf2.71 autoconf

closes: #12958

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: Illia Bobyr <illia.bobyr@gmail.com>
diff --git a/src/version.c b/src/version.c
index 9db8a01..bb6f52a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1823,
+/**/
     1822,
 /**/
     1821,