Require PHP 7.4 at least for running the build system (#9519)

Author: kocsismate

UPGRADING.INTERNALS

@@ -62,6 +62,8 @@ PHP 8.2 INTERNALS UPGRADE NOTES
 2. Build system changes
 ========================
 
+* The build system now requires PHP 7.4.0 at least. Previously PHP 7.1 was
+  required.
 * Unsupported libxml2 2.10.0 symbols are no longer exported on Windows.
 * Identifier names for namespaced functions generated from stub files through
   gen_stub.php have been changed. This requires that namespaced functions

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_stub.php is PHP 7.4.
+    if test "$php_version_num" -lt 70400; then
       AC_MSG_RESULT([$php_version (too old)])
       unset PHP
     else