Require PHP 7.4 at least for running the build system

Author: kocsismate

build/gen_stub.php

@@ -17,6 +17,10 @@
 error_reporting(E_ALL);
 ini_set("precision", "-1");
 
+if (PHP_VERSION_ID < 70400) {
+    throw new Exception("The build system requires PHP 7.4 at least.\n");
+}
+
 const PHP_70_VERSION_ID = 70000;
 const PHP_80_VERSION_ID = 80000;
 const PHP_81_VERSION_ID = 80100;

build/php.m4

@@ -1900,8 +1900,8 @@ AC_DEFUN([PHP_PROG_PHP],[
     set $php_version
     IFS=$ac_IFS
     php_version_num=`expr [$]{1:-0} \* 10000 + [$]{2:-0} \* 100 + [$]{3:-0}`
-    dnl Minimum supported version for gen_stubs.php is PHP 7.1.
-    if test "$php_version_num" -lt 70100; then
+    dnl Minimum supported version for gen_stubs.php is PHP 7.4.
+    if test "$php_version_num" -lt 70400; then
       AC_MSG_RESULT([$php_version (too old)])
       unset PHP
     else