Retiring GNU objdump 2.17.50

[Ed Maste]

We currently install and use at most three tools from GNU binutils
2.17.50, depending on target architecture:

1. as - assembler
2. ld - linker
3. objdump - diagnostic / information tool

I hope to retire all use of these obsolete binutils before FreeBSD 13.
Here I'd like to discuss objdump. It is a diagnostic tool that
provides information about object files, binaries and libraries. It's
not required as a bootstrap tool (i.e., not needed to build FreeBSD
world or kernel). It is required to build a limited number of ports,
and is used by some developers.

I have a tracking PR for GNU objdump's retirement open in PR 229046.
https://bugs.freebsd.org/229046.

There are two ways we can proceed with its retirement:

1. Remove it without replacement. Ports that need objdump to build
will have to depend on the binutils package/port, and users who wish
to use it will have to install it.

Related links for this path:
Ports exp-run: https://bugs.freebsd.org/212319
Patch review: https://reviews.freebsd.org/D7338

2. Install llvm-objdump in its place (perhaps via a symlink).
llvm-objdump is broadly compatible in both command-line argument
parsing and output format, but there are many small differences and
it's not a full drop-in replacement.

Related links for this path:
Patch review: https://reviews.freebsd.org/D18307

I am interested in feedback on the preferred approach. Installing
llvm's objdump has the advantage that for most use cases everything
will "just work", but may also introduce subtle failures.