unix: upgrade autoconf 2.69 -> 2.71

CPython 3.12 appears to require 2.71. To get 2.71 working we had to
define a new environment variable override.

Author: indygreg

cpython-unix/build-cpython.sh

@@ -23,6 +23,7 @@ export AUTOM4TE=${TOOLS_PATH}/host/bin/autom4te
 export autom4te_perllibdir=${TOOLS_PATH}/host/share/autoconf
 export AC_MACRODIR=${TOOLS_PATH}/host/share/autoconf
 export M4=${TOOLS_PATH}/host/bin/m4
+export trailer_m4=${TOOLS_PATH}/host/share/autoconf/autoconf/trailer.m4
 
 # The share/autoconf/autom4te.cfg file also hard-codes some paths. Rewrite
 # those to the real tools path.

pythonbuild/downloads.py

@@ -4,10 +4,10 @@
 
 DOWNLOADS = {
     "autoconf": {
-        "url": "https://ftp.gnu.org/gnu/autoconf/autoconf-2.69.tar.gz",
-        "size": 1927468,
-        "sha256": "954bd69b391edc12d6a4a51a2dd1476543da5c6bbf05a95b59dc0dd6fd4c2969",
-        "version": "2.69",
+        "url": "https://ftp.gnu.org/gnu/autoconf/autoconf-2.71.tar.gz",
+        "size": 2003781,
+        "sha256": "431075ad0bf529ef13cb41e9042c542381103e80015686222b8a9d4abef42a1c",
+        "version": "2.71",
     },
     # 6.0.19 is the last version licensed under the Sleepycat license.
     "bdb": {