[llvm-objcopy] Add elf32-sparc and elf32-sparcel target
The "sparc"/"sparcel" architectures appears in ArchMap (used by -B option) but not in OutputFormatMap (used by -I/-O option). Add their targets into OutputFormatMap for consistency.
Note that AFAIK there're no targets for 32-bit little-endian SPARC ("elf32-sparcel") in GNU binutils.
Reviewers: espindola, alexshap, rupprecht, jhenderson, compnerd, jakehehrlich
Reviewed By: jhenderson, compnerd, jakehehrlich
Subscribers: jyknight, emaste, arichardson, fedor.sergeev, jakehehrlich, MaskRay, llvm-commits
Differential Revision: https://reviews.llvm.org/D63238