Log Message:
deforaos-libsystem: update to 0.4.3

Changes since 0.4.2:
- API changes (version bump for libSystem.so)
- no longer build the tests by default
- bug fixes
- use XML to build documentation with Gtk-Doc

Changes specific to pkgsrc:
- use libtool to build libSystem.so

The latter should fix the build on macOS.