ZeroTier as a ReadyCloud replacement.

OK, so this is odd.  I just downgraded my 212 from 1.8.4 to 1.8.3 and then upgraded back to 1.8.4 and, while it gave me that warning, it did what I asked without needing to do anything else.  And apt list libstdc++6 says I only have the armel version, not the armhf one:  

root@RN212A:/data/Documents# apt list libstdc++6
Listing... Done
libstdc++6/now 4.9.2-10+deb8u2 armel [installed,local]

It does seem to imply I installed it locally.  I may have in my experiments to get the install to work before I discovered all (well, I guess not all) of the "secrets".

And if I try to install anything beyond 1.8.4, it complains about  openssl:armhf, not libstdc++6:armhf.

At this point, I just can't be of any more help.  The version you have still works, so you can stick with it until someone provides a solution.

I have seen one other possible solution through my Googling, but I'm reluctant to tell you to try it.  That's to install the package with dpkg, which doesn't automatically get the dependencies, then fix the dependencies with apt-get install -f.   I'm not sure where that will leave you if there are needed dependencies and apt-get doesn't fix them.