Our fix changed the baked-in gcc SDK reference from using the
MacOSX11.x and above to MacOSX.sdk. that fixes a number of broken
systems, but not all it appears.
Perhaps we should find a way to broaden that down to including
MacOSX10.15+ as well, if Catalina is going to be using the MacOSX11.x SDK.
Luckily it appears our previous fix was not responsible for this -- just
not broad enough to fix even more issues people have.
And -- baking the SDK into gcc at all is just a pain. It should just use
SDKROOT and it was supposed to do that after Iain's fixes.
Ken
