Log Message:
www/php-apcu: update to 5.1.18

Update php-apcu to 5.1.18.

o pkgsrc change: allow build with php74.

5.1.18		(2019-10-28)

- Implement apcu_inc() and apcu_dec() using atomic operations. This means
  that these functions no longer have to acquire a write lock. These
  functions will now wraparound on overflow, instead of saturating to a
  floating point value.
- Make table header in apc.php sticky.
- Fix compile warnings related to mktemp() usage.
- Fix compatibility with PHP 8.0.
- Fix required number of arguments for apcu_store() returned by Reflection.