specs: elide linkat tests with AT_SYMLINK_FOLLOW if necessary.
specs: elide linkat tests with AT_SYMLINK_FOLLOW if necessary.

On my Mac, running OS X 10.10, and using a local HFS+ volume, calling
linkat without AT_SYMLINK_FOLLOW returns ENOTSUPP.
* specs/posix_unistd_spec.yaml (linkat): If such a call returns
non-zero, skip the examples that would always fail.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

luaposix/luaposix