Fix the definition of the prlimit64 syscall

Fix the definition of the prlimit64 syscall

The `sys/resource.h` header adds #define-based redirection from
`prlimit64` to `prlimit` when `_GNU_SOURCE` is set. This causes our
`provided_syscalls` to incorrectly define `uk_syscall_r_prlimit` instead
of `uk_syscall_r_prlimit64`. By reordering, the headers we can side-step
this problem.

Signed-off-by: Marco Schlumpp <marco@unikraft.io>
Reviewed-by: Eduard Vintilă <eduard.vintila47@gmail.com>
Reviewed-by: Sergiu Moga <sergiu.moga@protonmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #41