Enable RTTI support for macOS

binding.gyp

{
  'targets': [
    {
      'target_name': 'bindings',
      'sources': [ 'bindings.cc' ],
      'cflags_cc!': [ '-fno-rtti' ],
      'conditions': [
        ['OS=="mac"', {
          'xcode_settings': {
            'GCC_ENABLE_CPP_RTTI': 'YES'
          }
        }]
      ]
    }
  ]
}