Using both --target-arch=armhf and --destructive-mode for my snap on my 18.04.1 LTS host results in “Sorry, an error occurred in Snapcraft”. The trace.txt file shows that the make plugin throws a NotImplementedError (“does not support cross-compiling to a different architecture”). I think that snapcraft v2.x printed this warning directly to STDOUT, so this might be a slight DX improvement.
Until the make plugin gains cross-compilation support, the instructions in “Request help troubleshoot cross compilation problem ” worked for me.