[php-src] Issue #8000: DateTime doesn't correctly parse PHP_INT_MIN timestamp

Issue: https://github.com/php/php-src/issues/8000 Comment Author: cmb69 The totally wrong PHP 8.0 behavior has been fixed in the latest timelib version, so PHP 8.1 yields better results; I don't think this fix will be backported. The "slightly" wrong PHP 8.1 behavior is due to timelib_get_signed_nr() calling [timelib_get_nr_ex()](https://github.com/derickr/timelib/blob/3183ed6a34a1982bd61577132034aaa36a1bddeb/parse_date.re#L467) to get the actual number (without the sign), and that function calls strtoull(3) which saturates to the largest possible positive value. A possible fix would be to let strtoull(3) parse the sign as well. Anyhow, this is actually an [upstream issue](https://github.com/derickr/timelib/issues); consider to report there, but see https://github.com/derickr/timelib/issues/108#issuecomment-820349578.