Support cases when using Rust conditional compilation

[fzyzcjy]

Changes

Close #1830

Checklist

• [ ] An issue to be fixed by this PR is listed above.
• [ ] New tests are added to ensure new features are working. Please refer to this page to see how to add a test.
• [ ] ./frb_internal precommit --mode slow (or fast) is run (it internal runs code generator, does auto formatting, etc).
• [ ] If this PR adds/changes features, documentations (in the ./website folder) are updated.
• [ ] CI is passing. Please refer to this page to see how to solve a failed CI.

Remark for PR creator

• ./frb_internal --help shows utilities for development.
• If fzyzcjy does not reply for a few days, maybe he just did not see it, so please ping him.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.24%. Comparing base (4e2992b) to head (ed7de6f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1856 +/- ## ======================================= Coverage 99.24% 99.24% ======================================= Files 366 366 Lines 15319 15319 ======================================= Hits 15204 15204 Misses 115 115 ```

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[TBG-FR]

Thanks a lot ! I will try that soon, you're awesome 🙌

[fzyzcjy]

Thanks and you are welcome!