ffi: default to reldbg when building iOS bindings

[Johennes]

Relates to: #4009

• [ ] Public API changes documented in changelogs (optional)

[codecov[bot]]

Codecov Report

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

Project coverage is 84.26%. Comparing base (746d7e1) to head (e73361e). Report is 3 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #4020 +/- ## ========================================== + Coverage 84.24% 84.26% +0.01% ========================================== Files 266 266 Lines 28349 28349 ========================================== + Hits 23884 23888 +4 + Misses 4465 4461 -4 ```

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