Support: Arrow Functions 2.0

[zonuexe]

https://wiki.php.net/rfc/arrow_functions_v2

• Target version: PHP 7.4
• Implementation: Add short closures / arrow functions php/php-src#3941
• Status: Accepted

$fn1 = fn($x) => $x + $y;