OSX and iOS support

[HarryR]

According to http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_system

#if defined(__unix__) || (defined(__APPLE__) && defined(__MACH__))

Support for running from memory on macOS works like:

https://github.com/CylanceVulnResearch/osx_runbin/blob/master/run_bin.c

This changes the executable type to MH_BUNDLE, but it uses a number of hardcoded magic strings and I don't know if they're portable across many versions, or if it'd work on iOS