Function wait 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn wait(stat_loc: *mut c_int) -> pid_t

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/wait.html.

Obtains status information pertaining to one of the caller’s child processes.

If returning because the status of a child process is available, returns a value equal to the process ID of the child process for which status is reported. If returning due to the delivery of a signal to the calling process, returns -1 and sets errno to EINTR. If otherwise failing, returns -1 and sets errno.