Classic confinement and core_dynamic_linker

[Joseph Rushton Wakeling]

Hello all,

Hearing about classic confinement was rather exciting given that it seems 
tailor-made for the use-cases of my current WiP snaps for the ldc2 D compiler 
and the dub D build system:
https://github.com/WebDrake/ldc2.snap/pull/1
https://github.com/WebDrake/dub.snap/pull/1

However, I'm running into difficulties every time I try to do a `snapcraft 
cleanbuild`: part-way through the build process I invariably get an error:

classic confinement requires the core_dynamic_linker to be set

I've discovered and tried the proposed workaround here:
https://bugs.launchpad.net/snapcraft/+bug/1650946/comments/11

... but it seems to make no difference.  Can anyone advise what else needs to be 
done to build a package with `classic` confinement?

My system is Ubuntu 16.04 with snapcraft 2.24 and snapd 2.20.1 (both installed 
from the normal Ubuntu apt repos).

Thanks & best wishes,

     -- Joe