objdump completion should suggest more filenames

[Marc Aldorasi <m101010a@xxxxxxxxx>]

zsh will not complete filenames for objdump unless the last argument is a
single option.  Instead, it will only autocomplete from the objdump options
list.  For example:

objdump <tab> (no options listed) will only complete options

objdump -d <tab> (single option at end) will complete filenames, as expected

objdump -dC (multiple options at end) will only complete options

objdump -d -C <tab> (single option at end) will complete filenames, as
expected

objdump -d -dC (multiple options at end) will only complete options

objdump -dC -d <tab> (single option at end) will complete filenames, as
expected

objdump -d a.out <tab> (filename at end) will only complete options

objdump -d -- <tab> (option separator at end) will only complete options

zsh should instead allow filename completions anywhere in the command, and
shouldn't allow option completions after --

This happens with both zsh 5.4.2 on x86_64 linux and zsh 5.4.1 on aarch64
android linux.