Fails to load on Windows

Tried to run bazel with io_bazel_rules_closure in GitHub Actions Windows-2019 environment and got
```
ERROR: C:/users/runneradmin/_bazel_runneradmin/h7l7fnou/external/io_bazel_rules_closure/third_party/png/BUILD:7:12: Executing genrule @io_bazel_rules_closure//third_party/png:libpng_k8 [for host] failed: (Exit 2): bash.exe failed: error executing command C:/Program Files/Git/usr/bin/bash.exe -c ... (remaining 1 argument(s) skipped)
tar: ./usr/lib/x86_64-linux-gnu/libpng12.so.0: Cannot create symlink to '/lib/x86_64-linux-gnu/libpng12.so.0': No such file or directory
```

I suspect that `third_party/png:libpng_k8` does not consider it is not in Linux environment.

Start with third_party/png/BUILD and the libpng_k8 genrule mentioned in the error, then reproduce the build in the GitHub Actions Windows-2019 environment. Check which Linux-specific assumptions cause the symlink failure; done means the target loads successfully on Windows without the reported bash or tar error.

Written by the indexing model from the issue text.