Reland [lld-macho] Fix bug in reading cpuSubType field.

This reverts commit 66692c82.

New changes:
  - update test to require aarch64
  - update test to not hard-code cpu[sub] type values (since they could change)
  - update test to temporarily skip windows (because llvm-mc on windows doesn't seem to work with triple arm64-apple-macos)

Differential Revision: https://reviews.llvm.org/D139572