reproducible builds: make build deterministic by adding explicit deps

Arnout Engelenrequested to merge
raboof/powerdevil:rb-plugins-rebased into master

Similar to https://qt-project.atlassian.net/browse/QTBUG-137440

To fix https://bugs.kde.org/show_bug.cgi?id=512867

I'll admit I don't quite know what I'm doing here, I'm mostly guessing and mimicking, but it does seem to remove the nondeterminism :)

Inspired in part by plasma-workspace!6075 (diffs)

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