Xcode update broke ports

[Ralph Castain]

Apple apparently included an Xcode update in a recent maintenance release.
Since the update, I am unable to run many of the compiler ports (gcc,
python) due to errors stating that system headers and libraries cannot be
found. Investigation revealed that the ports were all configured with:

--with-sysroot=/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk

However, the Xcode update apparently removed the MacOSX10.14.sdk in that directory and
replaced it with MacOSX10.15.sdk - even though I have NOT updated the OS
from Mojave!

I tried uninstalling all ports and reinstalling them, but that didn't
help. Ditto for simply creating a MacOSX10.14.sdk symlink.

Does anyone have a suggestion on how to get around this problem?

Ralph