[llvm-objcopy] Support full list of bfd targets that lld uses.
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.
Reviewers: jhenderson, jakehehrlich, espindola, alexshap, arichardson
Reviewed By: arichardson
Subscribers: fedor.sergeev, emaste, sdardis, krytarowski, atanasyan, llvm-commits, MaskRay, arichardson
Differential Revision: https://reviews.llvm.org/D60773