zc.buildout itself is fine. The z3c.recipe.sphinxdoc and z3c.recipe.tag recipes need to be upgraded to use the new system-Python friendly script generation, and then the mailman build should be fine. I'll see if I can get that recipe upgraded for you, but for now, removing those parts from your buildout.cfg makes it work for me.
I was able to dupe and investigate.
zc.buildout itself is fine. The z3c.recipe. sphinxdoc and z3c.recipe.tag recipes need to be upgraded to use the new system-Python friendly script generation, and then the mailman build should be fine. I'll see if I can get that recipe upgraded for you, but for now, removing those parts from your buildout.cfg makes it work for me.