[MachO] Add missing byte-swaps when reading dyld_info

Summary:
This fixes the following tests on big-endian hosts:

lld :: mach-o/dylib-install-names.yaml
lld :: mach-o/force_load-dylib.yaml
lld :: mach-o/lib-search-paths.yaml
lld :: mach-o/upward-dylib-load-command.yaml

Reviewers: lhames, kledzik, ruiu

Reviewed By: ruiu

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35022

llvm-svn: 307405