Previously, rb_getaddrinfo_a_before_exec() is called from before_exec().
However, the function needs to be called only before fork().
The change moves it to before_fork().
We need stop worker threads in getaddrinfo_a() before fork().
This change adds a hook before fork() that cancel all outstanding requests
and wait for all ongoing requests. Then, it waits for all worker
threads to be finished.
Fixes [Bug #17220]