math/saga: Update to 8.0.0

Major update with many new features, enhancements and bugfixes.

• Switch from autoconf to cmake
• wxWidgets >= v3.1 needed
• dev_tools and excercises enabled
• Tool numbers instead of library ones

Changelog: https://sourceforge.net/p/saga-gis/wiki/Changelog%208.0.0/attachment/changelog_saga_8.0.0.txt

Reported by: portscout