add note in UPGRADING

UPGRADING

@@ -594,6 +594,8 @@ PHP 8.1 UPGRADE NOTES
   . --with-password-argon2 now uses pkg-config to detect libargon2. As such,
     an alternative libargon2 location should now be specified using
     PKG_CONFIG_PATH.
+  . --with-external-libcrypt now allows to use system libcrypt/libxcrypt
+    instead in PHP own implementation.
 
 ========================================
 10. New Global Constants

ext/standard/config.m4

@@ -287,7 +287,7 @@ if test "$ac_cv_crypt_blowfish" = "no" || test "$ac_cv_crypt_des" = "no" || test
     AC_MSG_ERROR([Cannot use external libcrypt as some algo are missing])
    fi
 else
-  AC_DEFINE_UNQUOTED(PHP_USE_PHP_CRYPT_R, 0, [Whether PHP has to use its own crypt_r for blowfish, des and ext des])
+  AC_DEFINE_UNQUOTED(PHP_USE_PHP_CRYPT_R, 0, [Whether PHP has to use its own crypt_r])
 fi
 
 dnl