[lld-macho] Initial support for Linker Optimization Hints

Linker optimization hints mark a sequence of instructions used for
synthesizing an address, like ADRP+ADD. If the referenced symbol ends up
close enough, it can be replaced by a faster sequence of instructions
like ADR+NOP.

This commit adds support for 2 of the 7 defined ARM64 optimization
hints:
- LOH_ARM64_ADRP_ADD, which transforms a pair of ADRP+ADD into ADR+NOP
  if the referenced address is within +/- 1 MiB
- LOH_ARM64_ADRP_ADRP, which transforms two ADRP instructions into
  ADR+NOP if they reference the same page

These two kinds already cover more than 50% of all LOHs in
chromium_framework.

Differential Review: https://reviews.llvm.org/D128093