CFI: Fix encode_ty: unexpected 'CoroutineWitness'

Fix #122705 by adding support for encoding `ty:CoroutineClosure`.

Author: rcvalle

Diff for: compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -1349,6 +1349,13 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
             ty = transform_ty(tcx, fn_ptr, options);
         }
 
+        ty::CoroutineClosure(_, args) => {
+            // Transform async closures into function pointers
+            let fn_ptr = args.as_coroutine_closure().signature_parts_ty();
+            // Transform fn_sig inputs and output
+            ty = transform_ty(tcx, fn_ptr, options);
+        }
+
         ty::Ref(region, ty0, ..) => {
             // Remove references from function items, closures, Fn trait and Fn subtrait objects
             if ty0.is_fn_def()
@@ -1439,7 +1446,6 @@ fn transform_ty<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>, options: TransformTyOptio
 
         ty::Bound(..)
         | ty::Error(..)
-        | ty::CoroutineClosure(..)
         | ty::CoroutineWitness(..)
         | ty::Infer(..)
         | ty::Placeholder(..) => {

Diff for: tests/ui/sanitizer/cfi-async-closure-issue-122705.rs

@@ -0,0 +1,15 @@
+// Verifies that using async closure works.
+//
+//@ needs-sanitizer-cfi
+//@ compile-flags: -Clto -Cprefer-dynamic=off -Ctarget-feature=-crt-static -Zsanitizer=cfi -Copt-level=0 --edition=2021
+//@ run-pass
+
+#![feature(async_closure)]
+
+#[inline(never)]
+fn foo<T>(_: T) {}
+
+fn main() {
+    let a = async move |_: i32, _: i32| {};
+    foo(a);
+}