ViSQOL not compiling on mac (and workaround!)

Recent combinations of macOS/clang fail at building old versions of zlib (<1.3.1) - [example github issue](https://github.com/racket/racket/issues/5412).

Workaround:
```
$ TF_SYSTEM_LIBS=zlib bazel build :visqol -c opt
```

I had to first expunge my failed build:
```
$ bazel clean --expunge
```
Also, bazel on hombrew is too new and old versions there only go back to the 8.x line, I downloaded the version bazel suggested in the error message