Stabilize ADX target feature

This is a continuation of #60109, which noted that while the ADX
intrinsics were stabilized, the corresponding target feature never was.

This PR follows the same general structure and stabilizes the ADX target
feature.

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -148,7 +148,7 @@
 ];
 
 const X86_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
-    ("adx", Some(sym::adx_target_feature)),
+    ("adx", None),
     ("aes", None),
     ("avx", None),
     ("avx2", None),

compiler/rustc_feature/src/accepted.rs

@@ -51,6 +51,8 @@ macro_rules! declare_features {
     /// Allows the sysV64 ABI to be specified on all platforms
     /// instead of just the platforms on which it is the C ABI.
     (accepted, abi_sysv64, "1.24.0", Some(36167), None),
+    /// Allows using ADX intrinsics from `core::arch::{x86, x86_64}`.
+    (accepted, adx_target_feature, "1.61.0", Some(44839), None),
     /// Allows the definition of associated constants in `trait` or `impl` blocks.
     (accepted, associated_consts, "1.20.0", Some(29646), None),
     /// Allows using associated `type`s in `trait`s.

compiler/rustc_typeck/src/collect.rs

@@ -2689,7 +2689,6 @@ fn from_target_feature(
                 Some(sym::tbm_target_feature) => rust_features.tbm_target_feature,
                 Some(sym::wasm_target_feature) => rust_features.wasm_target_feature,
                 Some(sym::cmpxchg16b_target_feature) => rust_features.cmpxchg16b_target_feature,
-                Some(sym::adx_target_feature) => rust_features.adx_target_feature,
                 Some(sym::movbe_target_feature) => rust_features.movbe_target_feature,
                 Some(sym::rtm_target_feature) => rust_features.rtm_target_feature,
                 Some(sym::f16c_target_feature) => rust_features.f16c_target_feature,

library/core/src/lib.rs

@@ -207,7 +207,6 @@
 //
 // Target features:
 #![cfg_attr(bootstrap, feature(aarch64_target_feature))]
-#![feature(adx_target_feature)]
 #![feature(arm_target_feature)]
 #![feature(avx512_target_feature)]
 #![feature(cmpxchg16b_target_feature)]
@@ -219,6 +218,7 @@
 #![feature(sse4a_target_feature)]
 #![feature(tbm_target_feature)]
 #![feature(wasm_target_feature)]
+#![cfg_attr(bootstrap, feature(adx_target_feature))]
 
 // allow using `core::` in intra-doc links
 #[allow(unused_extern_crates)]