kcfi: add _NOCFI in kernel

[aokblast]

Summary

init_main.c mi_startup:
sys/vnet/vnet.c vnet_register_sysinit: call sip->func which is the sysinit function and the
callee should have the detailed type
kern_fork.c fork_exit: parameter callout should be fork_return only. Don't know
why it does not pass the check
subr_epoch.c epoch_call_task: all task callback have detailed type
kern_intr.c ithread_execute_handlers intr_event_handle taskrunner have the detailed type
subr_pctrie.c pctrie_reclaim_prune pctrie_reclaim_resume_compound
pctrie_reclaim_begin_compound:
radix.c rn_walktree: callback have detailed type and will
encapsulate more a higher layer
subr_syscall.c syscallenter: the syscall handler pack all arg into a
void ptr but the callee have the detailed type

[aokblast]

Repalace _NOCFI with __nosanitizerkcfi