The TargetData for this execution engine.

def target_data(self):
        """
        The TargetData for this execution engine.
        """
        if self._td is not None:
            return self._td
        ptr = ffi.lib.LLVMPY_GetExecutionEngineTargetData(self)
        self._td = targets.TargetData(ptr)
        self._td._owned = True
        return self._td