[llvm-objcopy] Support full list of bfd targets that lld uses.

Summary:
This change takes the full list of bfd targets that lld supports (see `ScriptParser.cpp`), including generic handling for `*-freebsd` targets (which uses the same settings but with a FreeBSD OSABI). In particular this adds mips support for `--output-target` (but not yet via `--binary-architecture`).

lld and llvm-objcopy use their own different custom data structures, so I'd prefer to check this in as-is (add support directly in llvm-objcopy, including all the test coverage) and do a separate NFC patch(s) that consolidate the two by putting this mapping into libobject.

See [[ https://bugs.llvm.org/show_bug.cgi?id=41462 | PR41462 ]].

Reviewers: jhenderson, jakehehrlich, espindola, alexshap, arichardson

Reviewed By: arichardson

Subscribers: fedor.sergeev, emaste, sdardis, krytarowski, atanasyan, llvm-commits, MaskRay, arichardson

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D60773

llvm-svn: 358562