addons: Add ** to special arches

[Fomys]

Per 1, ** is a valid keyword that can be used in pacakge.accept_keywords. Add it to the valid list so UnknownProfilePackageKeywords is not raised when using ** in a package.accept_keywords.

[ferringb]

Thanks, but this change isn't valid- the code as it is, is correct. See PMS rules on what is an allowed keyword https://projects.gentoo.org/pms/9/pms.html#keyword-names .

As to the confusion: ebuild KEYWORDS syntax carries both negation markers (-x86), and negated glob (-*). Negated keywords in the ebuild KEYWORDS don't have any real actual meaning beyond being used by devs and QA tools as an explicit statement of "stabilization for this architecture will never happen, ignore it".

For example, an ebuild that is just a 64bit x86 binary would have amd64 -*- the ebuild is only usable for amd64 arch, thus all other arches are marked as "can't be stabilized, ever". That is the sole reason a glob like operator is allowed in ebuild KEYWORDS- it avoids having to write amd64 -x86 -arm -whatever. Folks just use -* so the ebuild tree doesn't have to be updated every time a new arch comes along.

Considering above, ** has no meaning for ebuild KEYWORDS; that's strictly a package manager config hack for ACCEPT_KEYWORDS filtering logic.