I thought I would mention a tool I came across recently that might be of some use to people on this list who are sometimes tasked with making software runnable on older systems.
Deploymate <http://www.deploymateapp.com> scans source code for SDK dependencies, and will list certain MacOS SDK calls that don't meet a certain target. Handy for seeing what will and won't break on certain systems, and gives you the option of of #ifdef'ing things out or otherwise fixing the builds if you want to do so. So far seems much easier than the trial and error method I've used to date. Only real hiccup is that it requires an xcode project to scan, which sometimes means making an xcode project for a Makefile project. (A good system I found for doing that is here, btw: <https://hiltmon.com/blog/2015/08/01/simple-c-plus-plus-from-makefiles-to-xcode-builds/? Ken
