$DEVCACHE is observed to be 100k uncompressed; compressing it reduces
its size to ~5k. But compress it outside of `tar` so that archival
operation takes as little time as possible, to minimize the risk of
devices being created/removed during execution.
(From OE-Core rev: 571df6ddba1caa6805f7c96cd592eea399c2aee2)
Signed-off-by: Richard Tollerton <rich.tollerton@ni.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>