* Makefile (dist-separate): New variable.
(glibc-%.tar rule): Make separate tar files for add-ons listed there.
Depend on their configure files.
(dist-do-separate-dirs): New canned sequence to do that.
(dist-separate-libidn, dist-separate-linuxthreads): New variables.
(dist): Depend on add-on tar files based on $(dist-separate).
(dist-version): New variable, default to $(version).
(tag-for-dist, dist): Use that in place of $(version) in deps.