emerge -1a timezone-data --buildpkgonly These are the packages that would be built, in order: Calculating dependencies... done! Total: 0 packages, Size of downloads: 0 KiB WARNING: A requested package will not be merged because it is listed in package.provided: timezone-data pulled in by 'args' Nothing to merge; quitting. There is no way to force it? Reproducible: Always
There's no reason not to allow package.provided packages to be built (but not installed) with --buildpkgonly. So, it could be implicitly allowed with --buildpkgonly, with no need to force it.