CFI_PERMISSIVE should be disabled. Reacting with a kernel warning
is not enough.

Thanks to @thestinger for the idea.

Refers to #99.

This is what DEBUG_NOTIFIERS performs (see kernel/notifier.c):

```
#ifdef CONFIG_DEBUG_NOTIFIERS
		if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
			WARN(1, "Invalid notifier called!");
			nb = next_nb;
			continue;
		}
#endif
```

CFI can do the same better.

Thanks to @thestinger for the idea.

Refers to #99.

SCHED_STACK_END_CHECK checks the magic value at the end
of the kernel thread stack, and VMAP_STACK adds guard pages near it.
So they do a bit different things, but VMAP_STACK is more reliable.

Thanks to @thestinger for the idea.

Refers to #98.

Use f-strings.

That's important for the '--generate' mode.

Don't check CONFIG_ARCH_MMAP_RND_BITS if CONFIG_ARCH_MMAP_RND_BITS_MAX
was not found.

That improves debugging.

SCHED_CORE is finally available for ARM64 and ARM.

SCHED_SMT was needed for that.

Refers to #83

Thanks to @vobst for the idea