Display entry offset for .debug_names

Since commit ad6dde5 ("gdb/dwarf: write offset to parent entry for
DW_IDX_parent"), gdb now emits a .debug_names where the DW_IDX_parent
attribute refers to the parent entry's offset -- previously, due to
some confusion in the standard, gdb used the index of the parent's
name table entry.

This patch changes the .debug_names display code to display each
entry's offset.  This makes it easy to refer from a DW_IDX_parent to
the correct entry.

The new output looks like this:

[...]
Symbol table:
[  1] circular1: <0><1> DW_TAG_module DW_IDX_compile_unit=1 DW_IDX_die_offset=<0x19> DW_IDX_GNU_language=19
[...]
[  6] found: <0x28><2> DW_TAG_subprogram DW_IDX_compile_unit=1 DW_IDX_die_offset=<0x38> DW_IDX_GNU_language=19 DW_IDX_parent=<0x0>

Here you can see that DW_IDX_parent=0 refers to "circular1: <0>".

binutils/dwarf.c

@@ -10828,6 +10828,7 @@ display_debug_names (struct dwarf_section *section, void *file)
 	      uint64_t abbrev_tag;
 	      uint64_t dwarf_tag;
 	      const struct abbrev_lookup_entry *entry;
+	      uint64_t this_entry = entryptr - entry_pool;
 
 	      READ_ULEB (abbrev_tag, entryptr, unit_end);
 	      if (tagno == -1)
@@ -10840,9 +10841,9 @@ display_debug_names (struct dwarf_section *section, void *file)
 	      if (abbrev_tag == 0)
 		break;
 	      if (tagno >= 0)
-		printf ("%s<%" PRIu64 ">",
+		printf ("%s<%#" PRIx64 "><%" PRIu64 ">",
 			(tagno == 0 && second_abbrev_tag == 0 ? " " : "\n\t"),
-			abbrev_tag);
+			this_entry, abbrev_tag);
 
 	      for (entry = abbrev_lookup;
 		   entry < abbrev_lookup + abbrev_lookup_used;