Recommit "[llvm-objcopy][MachO] Support load commands used in executables/shared...

Recommit "[llvm-objcopy][MachO] Support load commands used in executables/shared libraries"

Summary:
This patch implements copying some load commands that appear in executables/shared libraries such as the indirect symbol table.

I don't add tests intentionally because this patch is incomplete: we need a layout algorithm for executables/shared libraries. I'll submit it as a separate patch with tests.

Reviewers: alexshap, rupprecht, jhenderson, compnerd

Reviewed By: alexshap

Subscribers: abrachet, mgorny, mgrang, MaskRay, mtrent, jakehehrlich, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D63395

llvm-svn: 369298