fix cfg related warnings (#485)

* remove mention of doc_cfg feature

`doc_cfg` has been superseded by `doc_auto_cfg`.

* allow `cfg(kani)`

Recently, rustc has started checking cfg expressions and so we have to
tell it explicitly that cfg(kani) is allowed because it has no way of
figuring that out itself.

Cargo.toml

@@ -47,3 +47,6 @@ pre-release-commit-message = "Bump version to {{version}}"
 push = false
 publish = false
 tag = false
+
+[lints.rust]
+unexpected_cfgs = { level = "warn", check-cfg = ['cfg(kani)'] }

src/instructions/interrupts.rs

@@ -146,10 +146,6 @@ pub fn int3() {
 /// It can also cause memory/register corruption depending on the interrupt
 /// implementation (if it expects values/pointers to be passed in registers).
 #[cfg(feature = "asm_const")]
-#[cfg_attr(
-    feature = "doc_cfg",
-    doc(cfg(any(feature = "nightly", feature = "asm_const")))
-)]
 pub unsafe fn software_interrupt<const NUM: u8>() {
     unsafe {
         asm!("int {num}", num = const NUM, options(nomem, nostack));