build: handle landlock feature as a tristate option

Yaakov Selkowitzrequested to merge
yselkowitz/tracker-miners:landlock into master

The kernel runtime test does not always work as intended for distribution builds. Instead, if the landlock feature is explicitly enabled, then just check that the header is present (meaning the code will compile). Only if the feature is auto, then check the kernel.

Closes: https://gitlab.gnome.org/GNOME/tracker-miners/-/issues/300

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