PR10499: Integrate attributes in dwarf_decl_file/line

PR10499: Integrate attributes in dwarf_decl_file/line

Elfutils prior to 0.143 didn't use attr_integrate when looking up the
decl_file or decl_line, so the attributes would sometimes be missed.
For those old versions, we define custom implementations to do the
integration.

* dwarf_wrappers.cxx (dwarf_decl_file_integrate): New.
  (dwarf_decl_line_integrate): New.
* dwarf_wrappers.h: Add macros to redirect calls to the above functions.
* dwflpp.cxx (dwflpp::iterate_over_labels): Replace a manual attribute
  lookup that is the same as dwarf_decl_line.