Add target_feature = "gc" for Wasm

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -266,6 +266,10 @@ pub(crate) fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> Option<LLVMFea
             "leoncasa" => Some(LLVMFeature::new("hasleoncasa")),
             s => Some(LLVMFeature::new(s)),
         },
+        Arch::Wasm32 | Arch::Wasm64 => match s {
+            "gc" if major < 22 => None,
+            s => Some(LLVMFeature::new(s)),
+        },
         Arch::X86 | Arch::X86_64 => {
             match s {
                 "sse4.2" => Some(LLVMFeature::with_dependencies(

compiler/rustc_target/src/target_features.rs

@@ -745,6 +745,7 @@ static WASM_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("bulk-memory", Stable, &[]),
     ("exception-handling", Unstable(sym::wasm_target_feature), &[]),
     ("extended-const", Stable, &[]),
+    ("gc", Unstable(sym::wasm_target_feature), &["reference-types"]),
     ("multivalue", Stable, &[]),
     ("mutable-globals", Stable, &[]),
     ("nontrapping-fptoint", Stable, &[]),

tests/ui/check-cfg/target_feature.stderr

@@ -121,6 +121,7 @@ LL |     cfg!(target_feature = "_UNEXPECTED_VALUE");
 `frecipe`
 `frintts`
 `fxsr`
+`gc`
 `gfni`
 `guarded-storage`
 `hard-float`