[llvm-objdump] Support arg grouping for -j and -M (e.g. llvm-objdump -sj.foo -dMreg-names-raw)

Summary:
r354375 added support for most objdump groupings, but didn't add support for -j|--sections, because that wasn't possible.
r354870 added --disassembler options, but grouping still wasn't available.
r355185 supported values for grouped options.

This just puts the three of them together. This supports -j in modes like `-s -j .foo`, `-sj .foo`, `-sj=.foo`, or `-sj.foo`, and similar for `-M`.

Reviewers: ormris, jhenderson, ikudrin

Reviewed By: jhenderson, ikudrin

Subscribers: javed.absar, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59618

llvm-svn: 356697