On this question we discussed the [linux][linux] and [unix][unix] tags being used to mark things that are specific to those OSes; [linux] posts only apply to linux, and [unix] posts only apply to unix. In practice that hasn't been happening; we even had a bunch of posts tagged with both, which makes little sense, but xeno went through and retagged them all
It is possible to blacklist tags as a last resort, but I'm still hoping enough of the community will handle retagging that it won't be an issue. It might be worth adding something in the tagtag wikiswikis for those tags, but I don't think it would help much
I don't think we should overload those tags to mean portability though; if a question is distro-specific I would expect it to be tagged with that distro's tag and with [linux]. Ideally I think tagging with the distro tag would automatically tag with [linux], since I can't see a way the former would be useful but not the latter, but there's currently no way to have automated tag dependencies (although it's been discussed in the past). I think your first example, [portable], might be a decent tag to represent portability