[llvm-objcopy][MachO] Support LC_LINKER_OPTIMIZATION_HINT load command

The load command is currently specific to arm64 and holds information
for instruction rewriting, e.g.  converting a GOT load to an ADR to
compute a local address.
(On ELF the information is usually conveyed by relocations, e.g.
R_X86_64_REX_GOTPCRELX, R_PPC64_TOC16_HA)

Reviewed By: alexander-shaposhnikov

Differential Revision: https://reviews.llvm.org/D104968