[php-src] Issue #7866: Ability to pick PHP value by reference in FFI.

Issue: https://github.com/php/php-src/issues/7866 Comment Author: KapitanOczywisty @userqq php itself is using these functions, so they should be loaded anyway - at this very moment I think this is the fastest and safest option. You can use callback variant, but ffi has quite a few issues with them. I think that string in FFI::cast should be treated as char[$strlen] or char*, thus FFI::cast('char*', $string) should be allowed. @cmb69 is this reasonable?