[compiler-rt] [compiler-rt] intercept macOs's freadlink call. (PR #83679)

[via llvm-commits]

expcov wrote:

This commit seems to have prevented builds on macOS Big Sur.

```
Undefined symbols for architecture arm64:
  "_freadlink", referenced from:
      _wrap_freadlink in tsan_interceptors_posix.cpp.o
      substitution_freadlink in tsan_interceptors_posix.cpp.o
     (maybe you meant: _wrap_freadlink)
ld: symbol(s) not found for architecture arm64
```

https://github.com/llvm/llvm-project/pull/83679