Display entry offset for .debug_names

Display entry offset for .debug_names

Since commit ad6dde5aaae ("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>".