patches: Use unikraft syscall in cxa_guard

patches: Use unikraft syscall in cxa_guard

This patch replaces calls to libc syscall() with short-circuited
unikraft-specific static implementations of these syscalls.

Co-authored-by: Marco Schlumpp <marco@unikraft.io>
Signed-off-by: Marco Schlumpp <marco@unikraft.io>
Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Razvan Deaconescu <razvand@unikraft.io>
Approved-by: Eduard Vintilă <eduard.vintila47@gmail.com>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #4