Bump minimum Autoconf requirement to 2.68

This patch syncs and bumps the minimum required version of Autoconf for
the `phpize.m4` script and the main `configure.ac` from previously mixed
2.64 and 2.59 to 2.68.

At the time of this writing Autoconf 2.63 is still the version on
Centos 6, however by the PHP 7.3 release current systems out there
should all have pretty much updated Autoconf versions to 2.64+ at
least. Centos 7 already has Autoconf 2.69, for example.

This provides more options to update and get current with the *nix
build system and also avoids broken builds in certain cases as pointed
out in the relevant discussion [1].

Additionally, phpize also already provides the `AX_CHECK_COMPILE_FLAG`
Autoconf Archive m4 file that has Autoconf 2.64 minimum requirement.

Autoconf 2.68 was released in 2010, 8 years ago, relative to this patch.

[1] https://github.com/php/php-src/pull/3562

build/buildcheck.sh

@@ -25,18 +25,18 @@ if test -z "$PHP_AUTOCONF"; then
   PHP_AUTOCONF='autoconf'
 fi
 
-# autoconf 2.64 or newer
+# autoconf 2.68 or newer
 ac_version=`$PHP_AUTOCONF --version 2>/dev/null|head -n 1|sed -e 's/^[^0-9]*//' -e 's/[a-z]* *$//'`
 if test -z "$ac_version"; then
 echo "buildconf: autoconf not found."
-echo "           You need autoconf version 2.64 or newer installed"
+echo "           You need autoconf version 2.68 or newer installed"
 echo "           to build PHP from Git."
 exit 1
 fi
 IFS=.; set $ac_version; IFS=' '
-if test "$1" = "2" -a "$2" -lt "64" || test "$1" -lt "2"; then
+if test "$1" = "2" -a "$2" -lt "68" || test "$1" -lt "2"; then
 echo "buildconf: autoconf version $ac_version found."
-echo "           You need autoconf version 2.64 or newer installed"
+echo "           You need autoconf version 2.68 or newer installed"
 echo "           to build PHP from Git."
 exit 1
 else

configure.ac

@@ -8,7 +8,7 @@ sinclude(Zend/acinclude.m4)
 dnl Basic autoconf + automake initialization, generation of config.nice.
 dnl -------------------------------------------------------------------------
 
-AC_PREREQ([2.64])
+AC_PREREQ([2.68])
 AC_INIT(README.GIT-RULES)
 ifdef([AC_PRESERVE_HELP_ORDER], [AC_PRESERVE_HELP_ORDER], [])
 

scripts/phpize.m4

@@ -1,6 +1,6 @@
 dnl This file becomes configure.ac for self-contained extensions.
 
-AC_PREREQ(2.59)
+AC_PREREQ([2.68])
 AC_INIT(config.m4)
 ifdef([AC_PRESERVE_HELP_ORDER], [AC_PRESERVE_HELP_ORDER], [])