I left all three dev boards running overnight – the PINE64 build (of 4.9.2) worked! that’s the first successful GCC build on any of the dev boards :-)
The Pi build failed – AH! I think it ran out of resources – and this is because I, like an idiot, have left “-j 4” in the build script! (which is fine for my laptop, but NOT fine for the dev boards).
The Ci20 stopped responding – and I wonder if this is also because of that.