rustc with correct version not working when compiling external/libgotcha

[yl3469]

Dear authors:

Thanks for providing such a good codebase! I really enjoyed the idea.
I have a question: When I did "make" under external/libgotcha, one issue pops up:

Could you help shed some light?

Thank you very much!

rustc -Clink-args="" --edition 2018 -Copt-level=2  --cfg 'stable="once_is_completed"' --crate-type lib --emit obj -o gotcha.o libgotcha.rs
error[E0658]: unions with non-`Copy` fields other than `ManuallyDrop<T>` are unstable
 --> handle.rs:5:125748
  |
5 | ...b union Dl_serinfo__bindgen_ty_1 { pub dls_serpath : __IncompleteArrayField < Dl_serpath > , pub __dls_serpath_pad : [ Dl_serp...
  |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #55149 <https://github.com/rust-lang/rust/issues/55149> for more information

error[E0204]: the trait `Copy` may not be implemented for this type
   --> goot.rs:269:17
    |
269 | #[derive(Debug, Copy, Clone)]
    |                 ^^^^
...
273 |     pub code: __IncompleteArrayField<u8>,
    |     ------------------------------------ this field does not implement `Copy`
    |
    = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0204]: the trait `Copy` may not be implemented for this type
 --> handle.rs:5:125694
  |
5 | ...rive ( Copy , Clone ) ] pub union Dl_serinfo__bindgen_ty_1 { pub dls_serpath : __IncompleteArrayField < Dl_serpath > , pub __d...
  |           ^^^^                                                  ------------------------------------------------------- this field does not implement `Copy`
  |
  = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to 3 previous errors