[llvm-objcopy] Handle -O <format> flag.
Summary:
The -O flag is currently being mostly ignored; it's only checked whether or not the output format is "binary". This adds support for a few formats (e.g. elf64-x86-64), so that when specified, the output can change between 32/64 bit and sizes/alignments are updated accordingly.
This fixes PR39135
Reviewers: jakehehrlich, jhenderson, alexshap, espindola
Reviewed By: jhenderson
Subscribers: emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D53667
llvm-svn: 350541