Fix: fix osx cp warning.

On macos, cp's `--no-preserve` option does not exist. It is enabled by default, and can be disabled with the explicit `-p` (preserve) flag.
This lead libsql-ffi's build.rs to warn about an illegal option used:

```
  cp: illegal option -- -
  usage: cp [-R [-H | -L | -P]] [-fi | -n] [-aclpSsvXx] source_file target_file
         cp [-R [-H | -L | -P]] [-fi | -n] [-aclpSsvXx] source_file ... target_directory
```

This changeset makes sure the option is only passed in non `macos` target_os.