patch 9.1.1664: configure: can use any autoconf

Problem:  configure: can use any autocon
Solution: Use AC_PREREQ and require 2.71 (Damien Lejay)

technically, we require autoconf 2.72, but that is not available on
Ubuntu LTS 24.04. So let's go with 2.71 for now and add a comment about
it in configure.ac

closes: #18047

Signed-off-by: Damien Lejay <damien@lejay.be>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/auto/configure

@@ -14507,18 +14507,18 @@ then :
 fi
 if test "$enable_largefile,$enable_year2038" != no,no
 then :
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CC option to enable large file support" >&5
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CPPFLAGS option for large files" >&5
-printf %s "checking for $CC option to enable large file support... " >&6; }
+printf %s "checking for $CPPFLAGS option for large files... " >&6; }
 if test ${ac_cv_sys_largefile_opts+y}
 then :
   printf %s "(cached) " >&6
 else case e in #(
-  e) ac_save_CC="$CC"
+  e) ac_save_CPPFLAGS=$CPPFLAGS
   ac_opt_found=no
-  for ac_opt in "none needed" "-D_FILE_OFFSET_BITS=64" "-D_LARGE_FILES=1" "-n32"; do
+  for ac_opt in "none needed" "-D_FILE_OFFSET_BITS=64" "-D_LARGE_FILES=1"; do
     if test x"$ac_opt" != x"none needed"
 then :
-  CC="$ac_save_CC $ac_opt"
+  CPPFLAGS="$ac_save_CPPFLAGS $ac_opt"
 fi
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -14547,12 +14547,12 @@ then :
   if test x"$ac_opt" = x"none needed"
 then :
   # GNU/Linux s390x and alpha need _FILE_OFFSET_BITS=64 for wide ino_t.
-	 CC="$CC -DFTYPE=ino_t"
+	 CPPFLAGS="$CPPFLAGS -DFTYPE=ino_t"
 	 if ac_fn_c_try_compile "$LINENO"
 then :
 
 else case e in #(
-  e) CC="$CC -D_FILE_OFFSET_BITS=64"
+  e) CPPFLAGS="$CPPFLAGS -D_FILE_OFFSET_BITS=64"
 	    if ac_fn_c_try_compile "$LINENO"
 then :
   ac_opt='-D_FILE_OFFSET_BITS=64'
@@ -14568,7 +14568,7 @@ fi
 rm -f core conftest.err conftest.$ac_objext conftest.beam conftest.$ac_ext
     test $ac_opt_found = no || break
   done
-  CC="$ac_save_CC"
+  CPPFLAGS=$ac_save_CPPFLAGS
 
   test $ac_opt_found = yes || ac_cv_sys_largefile_opts="support not detected" ;;
 esac
@@ -14592,16 +14592,14 @@ printf "%s\n" "#define _FILE_OFFSET_BITS 64" >>confdefs.h
 
 printf "%s\n" "#define _LARGE_FILES 1" >>confdefs.h
  ;; #(
-  "-n32") :
-    CC="$CC -n32" ;; #(
   *) :
     as_fn_error $? "internal error: bad value for \$ac_cv_sys_largefile_opts" "$LINENO" 5 ;;
 esac
 
 if test "$enable_year2038" != no
 then :
-  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CC option for timestamps after 2038" >&5
+  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for $CPPFLAGS option for timestamps after 2038" >&5
-printf %s "checking for $CC option for timestamps after 2038... " >&6; }
+printf %s "checking for $CPPFLAGS option for timestamps after 2038... " >&6; }
 if test ${ac_cv_sys_year2038_opts+y}
 then :
   printf %s "(cached) " >&6

src/configure.ac

@@ -1,14 +1,32 @@
-dnl configure.ac: autoconf script for Vim
+dnl +----------------------------------------------------------------------+
+dnl   configure.ac: autoconf script for Vim
+dnl +----------------------------------------------------------------------+
+dnl
+dnl   This file is processed by autoconf to generate the 'configure' script.
+dnl
+dnl   ==> IMPORTANT NOTE FOR DEVELOPERS <==
+dnl
+dnl   Do NOT run 'autoconf' directly on this file.  You must use the provided
+dnl   make target, like this:
+dnl
+dnl     make autoconf
+dnl
+dnl   This is required because the Makefile handles placing the generated
+dnl   script into its final location: 'auto/configure'.
+dnl
+dnl +----------------------------------------------------------------------+
 
-dnl Process this file with autoconf 2.72 to produce "configure".
+dnl You should use Autoconf 2.72 but to simplify CI on Ubuntu 24.04 we only
+dnl use AC_PREREQ([2.71])
+AC_PREREQ([2.71])
 
 dnl Normally, AC_INIT([package],[version],[bug-report],[tarname],[url])
 dnl provides PACKAGE_* macros, used by Autoconf on UNIX to inject version
 dnl info into config.h, --version output, and "make dist".
 dnl
-dnl Vim does not rely on that: versioning is centralized in version.h/version.c,
+dnl Vim does not rely on that: versioning is centralized in
-dnl which ensures a single cross-platform source of truth for both UNIX and
+dnl version.h/version.c, dnl which ensures a single cross-platform source of
-dnl non-UNIX platforms.
+dnl truth for both UNIX and non-UNIX platforms.
 dnl
 dnl Therefore we call AC_INIT without arguments.
 AC_INIT

src/version.c

@@ -724,6 +724,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1664,
 /**/
     1663,
 /**/