Supporting arm64 dyld_shared_cache

[samyk]

What would be required to get support for 64-bit? Perhaps I can help?

tigerblood:/Users/samy/Code/jb/misc-jevinskie$ ./dyld_decache ../ios-root/dyld_shared_cache_arm64
  0/1293: Dumping '/usr/lib/libSystem.B.dylib'...
Error: Cannot dump 'libraries/usr/lib/libSystem.B.dylib'. Only 32-bit little-endian single-file
       Mach-O objects are supported.
**** Failed: Undefined error: 0
  1/1293: Dumping '/usr/lib/libc++.1.dylib'...
Error: Cannot dump 'libraries/usr/lib/libc++.1.dylib'. Only 32-bit little-endian single-file
       Mach-O objects are supported.
**** Failed: Undefined error: 0