LLVM I/O benchmarks segfaulting on Mac

Feel free to close this if it's a duplicate / if the issue is known and ignored.

On my MBP M1, on both current `master`, and on Effekt v0.26, v0.25, v0.24, the I/O benchmarks `word_count_ascii` and `interleave_promises` don't work:
```
$ effekt --backend=llvm examples/benchmarks/input_output/word_count_ascii.effekt
[error] Process exited with non-zero exit code 139.
$ effekt --backend=llvm examples/benchmarks/input_output/interleave_promises.effekt
[error] Process exited with non-zero exit code 138.
```

It appears to be somewhat random whether the error is 138 or 139. :)

All other unignored benchmarks seem to work on LLVM.