See summary (mock doesn't catch unpackaged files :(). Patch attached.
Created attachment 122694 [details] Include unpackaged symlinks, rebuild against new slang
Thanks a lot, the build is on its way. BTW, I think it's rpm itself that doesn't complain about unpackaged symlinks by default, not just mach/mock.
rpm does nowadays, but mock is buggy (doesn't catch _any_ unpackaged files, even ordinary ones) and a fix is only in upstream CVS and not deployed anywhere AFAIK, see bug 163576.