gather: Don't pull multiple debuginfo packages
When there is a noarch subpackage, all compatible debuginfo would be
pulled in, which is not desirable.
Example: Server.x86_64 needs pkg.x86_64 and pkg-data.noarch. We only
want pkg-debuginfo.x86_64, but without this patch even
pkg-debuginfo.i686 would get in.
Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>