walk-nodes: add a tree type walker

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
ahaggar-ast: update the DECL_EXPR node

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>
ahhagar-ast: update CALL_EXPR and ADDR_EXPR nodes

Signed-off-by: Djalal Harouni <tixxdz@opendz.org>