Fix fs miri test on AArch64

src/tools/miri/tests/pass/shims/fs.rs

@@ -31,7 +31,7 @@ fn main() {
 }
 
 fn host_to_target_path(path: String) -> PathBuf {
-    use std::ffi::{CStr, CString};
+    use std::ffi::{c_char, CStr, CString};
 
     let path = CString::new(path).unwrap();
     let mut out = Vec::with_capacity(1024);