[llvm] [clang] [clang-tools-extra] [llvm-objcopy] Add --gap-fill and --pad-to options (PR #65815)

[James Henderson via cfe-commits]

https://github.com/jh7370 approved this pull request.

I'd like @MaskRay to give this a once-over before merging this, but otherwise LGTM.

https://github.com/llvm/llvm-project/pull/65815