util/disk_cache: Handle OS'es without d_type in struct dirent

This brings upstream a cleaned up version of a patch we've been carrying for a couple of years in the Solaris builds, since Solaris can't add d_type to struct dirent without breaking binary compatibility.

Fixes: f58e6fee ("util/disk_cache: delete more cache items in one go when full")
Signed-off-by: Alan Coopersmith alan.coopersmith@oracle.com