`g_get_system_data_dirs()`/`g_get_system_config_dirs()` don't ignore relative paths
The specification says:
All paths set in these environment variables must be absolute. If an implementation encounters a relative path in any of these variables it should consider the path invalid and ignore it.
but both GLib functions for system-wide lists ignore this part, and this leniency is made use of in tests.
The specification does not require adherency per se, but the documentation doesn't even mention this disobedience, so that users of this API would bear on the responsibility themselves.