Currently, torture.sh will compress the vmlinux files for KASAN and
KCSAN runs.  But it will compress all of the files, including those
copied verbatim by the kvm-again.sh script.  Compression takes around ten
minutes, so this is not a good thing.  This commit therefore compresses
only one of a given set of identical vmlinux files, and then hard-links
it to the directories produced by kvm-again.sh.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>