readelf -wf <file> would always crash on an external debug file. Now we
get:
```
> readelf -wf /usr/lib/debug/bin/cat.debug
The section .eh_frame contains:
readelf: dwarf_get_fde_list_eh failed: No entry found [dwarf_get_fde_list_eh(92)]
The section .debug_frame contains:
00000000 00000014 ffffffff CIE
Version: 4
Augmentation: ""
Code alignment factor: 1
Data alignment factor: -8
Return address column: 16
DW_CFA_def_cfa: r7 (rsp) ofs 8
DW_CFA_offset: r16 (rip) at cfa-8
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
DW_CFA_nop
...
```