Allow using fast destruction path when ASAN is in use

[danog]

Disabling the fast path when a custom allocator is in use hid the #18833 issue, and made it super hard to debug, this re-enables it if php is compiled with asan.

[danog]

Ping @nielsdos

[nielsdos]

By design, fast shutdown does not explicitly free all request data but defers that to ZendMM. If ZendMM is not used, but you use fast shutdown, then you get real leaks.
Therefore, your patch will report leaks with ASAN in non-debug builds.

[nielsdos]

A compromise could be to make it opt-in when __SANITIZE_ADDRESS__ is set. For example, you could have an environment variable similar to USE_ZEND_ALLOC, e.g. ZEND_FORCE_FAST_SHUTDOWN. Then you check if that environment variable is set along with !EG(full_tables_cleanup) probably.