cache: sync the cache file to disk in the background

This version uses a thread rather than a process, to avoid problems with
waitpid handling.  This gives slightly less overall build time reduction than
the separate process for it did (this reduces a -c compile coreutils-native by
about 3 seconds, while the process reduced it by 7 seconds), however this time
is quite insignificant relative to a typical build.

The biggest issue with non-backgrounded syncing is the perceived delay before
work begins, and this resolves that without breaking anything, or so it seems.

(Bitbake rev: 5ab6c5c7b007b8c77c751582141afc07c183d672)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

0 files changed, 0 insertions, 0 deletions