def-use: add correct edges to undefined functions
def-use: add correct edges to undefined functions

strip pointer casts only when it is constant expression,
otherwise add def-use edge to the top-level variable

Signed-off-by: Marek Chalupa <a05df156a69ad59faa9af9b666ef78009594c145@gmail.com>

mchalupa/dg,mchalupa/dg,mchalupa/dg,mchalupa/dg