PR25018, readelf crash on 32bits
Pointer comparisons after adding an offset just don't work to catch
overflow when the offset is a larger type than the pointer.
PR 25018
* dwarf.c (get_type_signedness): Delete ineffective pointer
comparison check. Properly range check uvalue offset on
recursive call.
(read_and_display_attr_value): Range check uvalue offset before
calling get_type_signedness.