macosx_deployment_target - building for previous versions from MacOS 10.13

[Friedrich Beckmann]

My strategy after all is

- Install everything I need to build pspp without macos_deployment_target set
- Set macos_deployment_target to 10.5 in macports.conf
- Force uninstall python38 and reinstall again
- Change macos_deployment_target to 10.7
- Fore uninstall the ports that provide the libraries for pspp. That is

   coreports="atk brotli bzip2 cairo expat fontconfig freetype fribidi \
     gdk-pixbuf2 gettext-runtime glib2 graphite2 gsl gtk3 gtksourceview3 \
     harfbuzz icu libepoxy libffi libiconv libpixman libpng libxml2 ncurses \
     ossp-uuid pango pcre readline spread-sheet-widget xz zlib“

- Install them again
- Install pspp
- Put all together in a bundle

Python38 is rebuild for 10.5 because some ports check python with introspection and
figure out a higher deployment target. Then they do not build. I build python for 10.5
because the python38 build fails for 10.6 and 10.7. See:

  https://trac.macports.org/ticket/58882#comment:43

The setup of the build environment is scripted here:

  https://github.com/fredowski/osxbundler/blob/master/installmacports.sh

and the build of the pspp bundle is here:

  https://github.com/fredowski/osxbundler/blob/master/buildpspp.sh

The build environment is fixed with a checkout of the macports-ports containing all ports as a source in sources.conf.

Thanks for your help!