Require PHP 8.1 in configure

Author: onethumb

config.m4

@@ -21,8 +21,8 @@ if test "$PHP_CRC_FAST" != "no"; then
     AC_MSG_ERROR([failed to detect PHP version, please report])
   fi
 
-  if test "$php_version" -lt "80000"; then
-    AC_MSG_ERROR([You need at least PHP 8.0.0 to be able to use this version of crc_fast. PHP $php_version found])
+  if test "$php_version" -lt "80100"; then
+    AC_MSG_ERROR([You need at least PHP 8.1.0 to be able to use this version of simdutf. PHP $php_version found])
   else
     AC_MSG_RESULT([$php_version, ok])
   fi