Add fixme tests for issue rust-lang#2121 (rust-lang#2122)

Add fixme tests for rust-lang#2121 to the expected suite since the test should fail, but not crash.

tests/expected/intrinsics/ctpop_ice_fixme/expected

@@ -0,0 +1 @@
+Kani unexpectedly panicked during compilation.

tests/expected/intrinsics/ctpop_ice_fixme/fixme_ctpop_ice.rs

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+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+//! Check that we correctly handle type mistmatch when the argument is a ZST type.
+//! The compiler crashes today: https://github.com/model-checking/kani/issues/2121
+
+#![feature(core_intrinsics)]
+use std::intrinsics::ctpop;
+
+// These shouldn't compile.
+#[kani::proof]
+pub fn check_zst_ctpop() {
+    let n = ctpop(());
+    assert!(n == ());
+}

tests/expected/intrinsics/sub_with_workflow_ice_fixme/arithmetic_zst_fixme.rs

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+// Copyright Kani Contributors
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+//! Check that arithmetic operations with overflow compilation fails.
+//! The compiler crashes today: https://github.com/model-checking/kani/issues/2121
+
+#![feature(core_intrinsics)]
+use std::intrinsics::sub_with_overflow;
+
+#[kani::proof]
+pub fn check_zst_sub_with_overflow() {
+    let n = sub_with_overflow((), ());
+    assert!(!n.1);
+}

tests/expected/intrinsics/sub_with_workflow_ice_fixme/expected

@@ -0,0 +1 @@
+Kani unexpectedly panicked during compilation.