Add dwarf2_per_cu_data::addresses_seen

This adds a new member to dwarf2_per_cu_data that indicates whether
addresses have been seen for this CU.  This is then set by the
.debug_aranges reader.  The idea here is to detect when a CU does not
have address information, so that the new indexer will know to do
extra scanning in that case.

gdb/dwarf2/read.c

@@ -2740,6 +2740,8 @@ read_addrmap_from_aranges (dwarf2_per_objfile *per_objfile,
 		 - baseaddr);
 	  addrmap_set_empty (mutable_map, start, end - 1, per_cu);
 	}
+
+      per_cu->addresses_seen = true;
     }
 
   return true;