[Samba] Flushing wafcache when tweaking Samba builds

[Nico Kadel-Garcia]

I notice that Sama builds with Samba 4.0.x now use WAFCACHE to store
temporary files in the build process. Caching these files is fine, but
what clears them out? I've been working in test environments where
WAFCACHE was set to "/tmp/wafcache", such as building Fedora RPM's for
testing, and eventually ran my filesystem out of inodes because
nothing expires them.

For now, I've left a cron job running to flush old files there, but
does anyone have a better approach? Should the WAFCACHE be in inside
the build tree, and flushed as part of "make clean"?