"rust-intrinsic" ABI and `#[rustc_intrinsic_must_be_overridden]` support has been removed from the compiler

[Skgland]

It came up in rust-lang/rust#132735 that support for #[rustc_intrinsic_must_be_overridden] has been removed from rustc but is still present in rust-analyzer.
It was suggested rust-lang/rust#132735 (comment) to open an issue here.

Relevant sections of code are

• rust-analyzer/crates/hir-expand/src/inert_attr_macro.rs

  Lines 643 to 646 in c588273

  	rustc_attr!(
  	rustc_intrinsic_must_be_overridden, Normal, template!(Word), ErrorFollowing,
  	"the `#[rustc_intrinsic_must_be_overridden]` attribute is used to declare intrinsics without real bodies",
  	),

• rust-analyzer/crates/hir-ty/src/mir/eval/shim.rs

  Line 85 in c588273

  || attrs.by_key(&sym::rustc_intrinsic_must_be_overridden).exists(),

• rust-analyzer/crates/intern/src/symbol/symbols.rs

  Line 447 in c588273

  rustc_intrinsic_must_be_overridden,

"rust-intrinsic" support had been removed a bit hastily in rust-lang/rust@51b51b5 which has been reverted in rust-lang/rust#139496

[Veykril]

Noting down the PR that removed this will land with 1.87, so it will be a while until we drop support for this.

[Veykril]

Once we do remove this, we can remove the rust-intrinsic support with it as well (which needs a 1.86 bump), cc rust-lang/rust#139455