geography/qgis: Adapt to new USE_LANGUAGES scheme

Demote c++17 to c++ in USE_LANGUAGES and add USE_CXX_FEATURES.
PKGREVISION++ because I'm not entirely sure there are no changes.
(qgis is not documented to require setting -std flags, or even really
to need a c++17 compiler, but the CMakeFiles say that it does.  Raised
upstream with no response.)

(gdt)