Rollup merge of #124067 - RalfJung:weak-lang-items, r=davidtwco

weak lang items are not allowed to be #[track_caller]

For instance the panic handler will be called via this import
```rust
        extern "Rust" {
            #[lang = "panic_impl"]
            fn panic_impl(pi: &PanicInfo<'_>) -> !;
        }
```
A `#[track_caller]` would add an extra argument and thus make this the wrong signature.

The 2nd commit is a consistency rename; based on the docs [here](https://doc.rust-lang.org/unstable-book/language-features/lang-items.html) and [here](https://rustc-dev-guide.rust-lang.org/lang-items.html) I figured "lang item" is more widely used. (In the compiler output, "lang item" and "language item" seem to be pretty even.)

compiler/rustc_feature/src/builtin_attrs.rs

@@ -798,7 +798,7 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // ==========================================================================
     gated!(
         lang, Normal, template!(NameValueStr: "name"), DuplicatesOk, EncodeCrossCrate::No, lang_items,
-        "language items are subject to change",
+        "lang items are subject to change",
     ),
     rustc_attr!(
         rustc_pass_by_value, Normal, template!(Word), ErrorFollowing,