Building on 10.15

[adamwolf]

I dug into this over the weekend. Python compilation fails, but in fact, Python compilation of all Python 3 and all Python 2 seems to fail! Everyone sees it too:
https://trac.macports.org/ticket/58882

A workaround is to set the min deploy version to 10.14. I made that build and now need to run it on 10.15 (and 10.14, actually!)

[adamwolf]

I cannot build a DMG on 10.15 right now. The template image runs out of space. I have seen folks saying that sparsebundles and bundle handling is different in 10.15.