Make tests pass on old macos
Make tests pass on old macos

On old macos systems, `fs::hard_link()` will follow symlinks.
This changes the test `symlink_hard_link` to exit early on
these systems, so that tests can pass.

graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust