add `unwind_asm` feature gate for `may_unwind` option

compiler/rustc_ast_lowering/src/asm.rs

@@ -49,6 +49,17 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 .struct_span_err(sp, "the `att_syntax` option is only supported on x86")
                 .emit();
         }
+        if asm.options.contains(InlineAsmOptions::MAY_UNWIND)
+            && !self.sess.features_untracked().asm_unwind
+        {
+            feature_err(
+                &self.sess.parse_sess,
+                sym::asm_unwind,
+                sp,
+                "the `may_unwind` option is unstable",
+            )
+            .emit();
+        }
 
         let mut clobber_abis = FxHashMap::default();
         if let Some(asm_arch) = asm_arch {

compiler/rustc_feature/src/active.rs

@@ -290,6 +290,8 @@ declare_features! (
     (active, asm_experimental_arch, "1.58.0", Some(72016), None),
     /// Allows using `sym` operands in inline assembly.
     (active, asm_sym, "1.58.0", Some(72016), None),
+    /// Allows the `may_unwind` option in inline assembly.
+    (active, asm_unwind, "1.58.0", Some(72016), None),
     /// Allows the user of associated type bounds.
     (active, associated_type_bounds, "1.34.0", Some(52662), None),
     /// Allows associated type defaults.

compiler/rustc_span/src/symbol.rs

@@ -332,6 +332,7 @@ symbols! {
         asm_const,
         asm_experimental_arch,
         asm_sym,
+        asm_unwind,
         assert,
         assert_inhabited,
         assert_macro,

src/test/ui/feature-gates/feature-gate-asm_unwind.rs

@@ -0,0 +1,8 @@
+#![feature(asm)]
+
+fn main() {
+    unsafe {
+        asm!("", options(may_unwind));
+        //~^ ERROR the `may_unwind` option is unstable
+    }
+}

src/test/ui/feature-gates/feature-gate-asm_unwind.stderr

@@ -0,0 +1,12 @@
+error[E0658]: the `may_unwind` option is unstable
+  --> $DIR/feature-gate-asm_unwind.rs:5:9
+   |
+LL |         asm!("", options(may_unwind));
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #72016 <https://github.com/rust-lang/rust/issues/72016> for more information
+   = help: add `#![feature(asm_unwind)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.