click.cc: Update sched-related functions

click.cc: Update sched-related functions

Update the sched-related functions to match the changes to the Unikraft
core. Update the thread creation functions and change the `thread_wait`
function to a loop that waits for the thread to end.

Signed-off-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #7