Function syscall_from_register_arguments_trd64bit 

pub fn syscall_from_register_arguments_trd64bit(
    syscall_number: u8,
    r0: usize,
    r1: MachineRegister,
    r2: MachineRegister,
    r3: MachineRegister,
) -> Option<Syscall>

Helper function for converting raw values passed back from an application into a Syscall type.

This implements a 64-bit ABI.