As-of https://github.com/Homebrew/homebrew-portable-ruby/pull/100 we've
removed ARM builds for Portable Ruby due to months of breakage.
Similarly, when we last bumped Portable Ruby the ARM build was much
delayed but, despite Homebrew/brew being completely unusable to anyone
using it on ARM in that case, no-one complained or filed issues.
Instead of attempting to maintain and update a Portable Ruby on niche
(Homebrew) platforms like ARM (or, in past/future PPC) improve the
messaging to provide users with a workaround.
Now we allow only a major/minor version match it should be pretty
doable for those users to install e.g. a prebuilt Ruby binary from a PPA
or built it from source if needed using `ruby-build` and `rbenv`.
The messaging could be improved further but we're somewhat limited by
`ruby.sh` and `vendor-install.sh` being separate. I'm tempted to combine
them (or at least have `vendor-install.sh` not be so generic as to not
be able to give Ruby-specific advice).
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