This commit adds the sign method to Payload::MachO which performs a
basic SHA256 signature update on the provided macho to enable it to run
under osx aarch64 systems.
This builds on Back from the dyld by adding the required aarch64
assembly code to enable the OSX loader to run on the m1. This enables
the use of native payloads on M1 or M2 devices that do not have Rosetta
installed.