ppc64le support in 9.3 branch?

So I see somebody at 2ndQ has set up a bunch of ppc64le buildfarm
members, which I applaud. But they're all failing on the 9.3 branch,
because we lack support for that architecture in that branch.

Does anyone have the stomach for trying to add such support? The minimum
requirement would be to back-patch 9.4's config.guess and config.sub,
because that's where the builds are falling over right now. I wouldn't be
too afraid of that, but what is not clear is what portability issues might
be lurking beyond that. I could not find any specific mention of ppc64
in the git changelogs, but that doesn't mean there weren't any other 9.4
fixes that might need to be back-ported.

It's hard to justify putting in very much effort to add new-platform
support in a branch that's scheduled to die in six months, so I'm not
sure what to do. Should we just tell 2ndQ not to bother running those
animals on 9.3? Or should we make at least a bit of effort towards
making it work?

The compromise I'm inclined to offer is to see what happens if we
back-patch 9.4's config.guess and config.sub. If that makes these
animals go green, and doesn't break any others, we'll call it good.
Otherwise, we revert that change and say we're not putting any
additional effort into it.

regards, tom lane