Add support for zen and zen2
Enable more fallbacks for zen and zen2
Adds Zen and Zen2 binaries, stripped
Built with gcc 9.3.0
Other binaries will be added if testing shows improvement
Fix hangs in mbuild-all.sh build script
Add silvermont and goldmont to build script, untested, support TBD
GMP is GPLv2
More info: http://zzz.i2p/topics/2955