stat: illegal option -- c

When running the tests for jsonnet 0.17.0 on macOS 10.13.6 (`./tests.sh`), this is printed:
```
stat: illegal option -- c
usage: stat [-FlLnqrsx] [-f format] [-t timefmt] [file ...]
stat: illegal option -- c
usage: stat [-FlLnqrsx] [-f format] [-t timefmt] [file ...]
```
I guess `-c` is a GNU-specific extension of stat. macOS uses BSD stat, not GNU stat.