Add regression test for model-checking/kani#21 (rust-lang#22)

Author: danielsn

rust-tests/cbmc-reg/Cast/fixme_path.rs

@@ -0,0 +1,7 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+use std::path::Path;
+
+fn main() {
+    let path = Path::new("./foo/bar.txt");
+}