aarch64/arm builders

[Christian Hergert <christian hergert me>]

The arm/aarch64 SDK builders on gnome-nightly seem to be about a year
out of date. Are there plans to get these updated, or is that blocking
on BuildStream? Maybe we just forgot about them?

I'm trying to get the final touches fixed in Builder for 3.28 that
allows building for ARM (so that we can support the Purism phone).

Having a 3.28 SDK is perfectly fine, it doesn't have to be master.
Perhaps that's in the plan already, given that we have a 3.26 which
appears to be newer than the SDKs on gnome-nightly.

-- Christian