Copy inline helpers for the cached variant of the rbtree, not used yet.
Rename 'new' for C++ compatibility.
Signed-off-by: David Sterba <dsterba@suse.com>
In order to use rb_root_cached we need to sync with kernel sources. Copy
the file from linux.git/include/linux/rbtree_types.h and update so it's
C++ protected for inclusion to libbtrfs and remove duplicate
definitions.
Signed-off-by: David Sterba <dsterba@suse.com>