Auto merge of rust-lang#83908 - Flying-Toast:master, r=davidtwco

Add enum_intrinsics_non_enums lint

There is a clippy lint to prevent calling [`mem::discriminant`](https://doc.rust-lang.org/std/mem/fn.discriminant.html) with a non-enum type. I think the lint is worthy of being included in rustc, given that `discriminant::<T>()` where `T` is a non-enum has an unspecified return value, and there are no valid use cases where you'd actually want this.

I've also made the lint check [variant_count](https://doc.rust-lang.org/core/mem/fn.variant_count.html) (rust-lang#73662).

closes rust-lang#83899

Author: bors

core/src/mem/mod.rs

@@ -1053,6 +1053,7 @@ pub const fn discriminant<T>(v: &T) -> Discriminant<T> {
 #[inline(always)]
 #[unstable(feature = "variant_count", issue = "73662")]
 #[rustc_const_unstable(feature = "variant_count", issue = "73662")]
+#[rustc_diagnostic_item = "mem_variant_count"]
 pub const fn variant_count<T>() -> usize {
     intrinsics::variant_count::<T>()
 }