- prioritise the first `pod2man` in the `PATH` if possible. This shim
was created to handle the case where there isn't one but, if there is,
we want to allow e.g. using a `pod2man` dependency to override the use
of the system version
- make `/usr/bin/pod2man` lower priority but still prioritise it over
a Homebrew-installed `pod2man` that's not in the `PATH` unless it
doesn't exist.
This shim was originally added in
5c973bad7422cf7f335e952a91ddfa2273aa2e4f to workaround a missing
`/usr/bin/pod2man`. It's now unfortunately resulting in using an older
`pod2man` on newer macOS versions.
Instead, let's use `/usr/bin/pod2man` if it's available and, if not,
work backwards to find the newest available version that is available.
