ZPP Fail on Overflow

WIP patch for this RFC: https://wiki.php.net/rfc/zpp_fail_on_overflow
bwoebi pointed out that I should check for `(double)(ZEND_LONG_MAX + 1)` on 32-bit as `(double)(ZEND_LONG_MAX + 0.5)` wouldn't truncate. I should probably \#if this.